A Look up A at Dictionary.com
first letter of the Roman alphabet, based on Greek alpha (see alpha). In music from c. 1600 as the name of the sixth note of the natural scale; it is the note given by a fixed-tone instrument (usually oboe or organ) to which all the instruments of an orchestra are tuned. As a blood type, 1926, denoting A agglutinogens. The A side of a two-sided record (by 1962, see side (n.)) held the material chosen for promotion. A-bomb, short for atom bomb, was in newspaper headlines by Aug. 8, 1945.
a (1) Look up a at Dictionary.com
indefinite article, form of an used before consonants, mid-12c., a weakened form of Old English an "one" (see an). The disappearance of the -n- before consonants was mostly complete by mid-14c. After c. 1600 the -n- also began to vanish before words beginning with a sounded -h-; it still is retained by many writers before unaccented syllables in h- or (e)u- but is now no longer normally spoken as such. The -n- also lingered (especially in southern England dialect) before -w- and -y- through 15c.

It also is used before nouns of singular number and a few plural nouns when few or great many is interposed.
a (2) Look up a at Dictionary.com
as in twice a day, etc., a reduced form of Old English an "on" (see on (prep.)), in this case "on each." The sense was extended from time to measure, price, place, etc. The habit of tacking a onto a gerund (as in a-hunting we will go) was archaic after 18c.
a capella Look up a capella at Dictionary.com
1876, earlier alla capella (1847), from Italian, "in the style of Church music, in the manner of the chapel," literally "according to the chapel," from cappella "chapel" (see chapel). Originally in reference to older church music (pre-1600) which was written for unaccompanied voices; applied 20c. to unaccompanied vocal music generally. Italian a is from Latin ad "to, according to" (see ad-); alla is a la "to the."
a deux Look up a deux at Dictionary.com
French, à deux, literally "for two," from à, from Latin ad (see ad-) + deux (see deuce). By 1876 as a French term in English.
a la Look up a la at Dictionary.com
from French à la, literally "to the," hence "in the manner of, according to," from à, from Latin ad "to" (see ad-) + la, fem. of definite article le "the," from Latin ille (fem. illa). Attested in English in French terms from fashion or cookery since late 16c.; since c. 1800 used in native formations with English words or names.
a la carte Look up a la carte at Dictionary.com
"ordered by separate items" (itemized on a bill); distinguished from a table d'hôte, indicating a meal served at a fixed, inclusive price; 1826, from French à la carte, literally "by the card" (see a la + card (n.1)).
a la mode (adv.) Look up a la mode at Dictionary.com
also alamode, 1640s, from French à la mode (15c.), literally "in the (prevailing) fashion" (see a la + mode (n.2)). In 17c., sometimes nativized as all-a-mode. Cookery sense in reference to a dessert served with ice cream is 1903, American English; earlier it was used of a kind of beef stew or soup (1753).
a posteriori Look up a posteriori at Dictionary.com
17c., in reference to reasoning from a consequent to its antecedent, from an effect to its cause; Latin, literally "from what comes after;" from a, usual form of ab "off, of, away from" before consonants (see ab-) + posteriori, neuter ablative of posterius, comparative of posterus "after, subsequent," from post "after" (see post-). Opposed to a priori. In modern use (from c. 1830, based on Kant) roughly equivalent to "from experience."
a priori Look up a priori at Dictionary.com
1710, "from cause to effect," a Latin term in logic from c. 1300, in reference to reasoning from antecedent to consequent, based on causes and first principles, literally "from what comes first," from priori, ablative of prior "first" (see prior (adj.)). Opposed to a posteriori. Since c. 1840, based on Kant, used more loosely for "cognitions which, though they may come to us in experience, have their origin in the nature of the mind, and are independent of experience" [Century Dictionary]. Related: Apriorist; apriorism; aprioristic.

The a is the usual form of Latin ab "off, of, away from" before consonants (see ab-). It is also the source of the à in Thomas à Kempis.
A&P Look up A&P at Dictionary.com
original U.S. grocery chain and leading food retailer of the mid-20c., the abbreviation by 1875, originally The Great Atlantic and Pacific Tea Company, which grew out of a New York firm founded 1859 by George Gilman and subsequently expanded by George Huntington Hartford. It ceased operation in 2015.
a- (2) Look up a- at Dictionary.com
prefix meaning "away," from Latin a, usual form of Latin ab "off, of, away from" before consonants (see ab-). As in avert, avocation.
a- (3) Look up a- at Dictionary.com
prefix meaning "not," from Greek a-, an- "not" (the "alpha privative"), from PIE root *ne "not" (source also of Latin nil, English un- (q.v.)). In words from Greek, such as abyssmal, adamant, amethyst; also partly nativized as a prefix of negation (asexual, amoral, agnostic).
a- (1) Look up a- at Dictionary.com
prefix or inseparable particle, a relic of various Germanic and Latin elements. In words derived from Old English, it most commonly represents Old English an "on" (see on (prep.)), as in alive, asleep, aback, abroad, afoot, ashore, ahead, abed, aside, apart, etc., forming adjectives and adverbs from nouns. It is identical to a (2).

It also can represent Middle English of, as in anew, afresh, akin, abreast. Or it can be a reduced form of the Old English past participle prefix ge-, as in aware. Or it can be the Old English intensive a-, as in arise, awake, ashame, marking a verb as momentary, a single event.

In words from Romanic languages, often it represents reduced forms of Latin ad- "to, at" (see ad-), or ab- "from, away, off" (see ab-); both of which by about 7c. had been reduced to a- in the ancestor of Old French.
[I]t naturally happened that all these a- prefixes were at length confusedly lumped together in idea, and the resultant a- looked upon as vaguely intensive, rhetorical, euphonic, or even archaic, and wholly otiose. [OED]
A-1 Look up A-1 at Dictionary.com
also A1, A-one, "first-rate," 1837 (in Dickens); a figurative use from Lloyd's of London marine insurance company's system for selective rating of merchant vessels ("Register of British and Foreign Shipping"), where it is the designation for ships in first-class condition. The letter refers to the condition of the hull of the ship itself, and the number rating to the equipment. Also used in equivalent ratings in U.S., where colloquially it is sometimes expanded to A No. 1.
A-frame Look up A-frame at Dictionary.com
type of framework shaped like the capital letter "A," 1909; as a type of building construction in this shape from 1932.
A-line (adj.) Look up A-line at Dictionary.com
descriptive of a dress or skirt flared in shape of a capital letter "A," 1955, in reference to the creations of French fashion designer Christian Dior (1905-1957).
A-list (adj.) Look up A-list at Dictionary.com
in celebrity sense, 1984, from A in the sense of "first, best" (as in A-1) + list (n.1).
A-OK Look up A-OK at Dictionary.com
1961, said to be an abbreviation of all (systems) OK; popularized in the jargon of U.S. astronauts. See OK.
A.A. Look up A.A. at Dictionary.com
also AA, abbreviation of Alcoholics Anonymous, attested by 1941, American English. The group name was the title of a book published in 1938 by the founder, Bill W. From 1914 as an abbreviation of anti-aircraft guns.
A.A.A. Look up A.A.A. at Dictionary.com
also AAA, abbreviation of American Automobile Association, attested 1902, American English, the year the organization was founded.
A.B. Look up A.B. at Dictionary.com
affixed to a name, abbreviation of Modern Latin Artium Baccalaureus "Bachelor of Arts" (see bachelor), 1773, American English. British English preferred B.A.. A.B. was used in Britain to mean able-bodied on seamen's papers.
A.D. Look up A.D. at Dictionary.com
1570s, an abbreviation of Latin Anno Domini "Year of the Lord." This system of counting years was put forth by Dionysius Exiguus in 527 or 533 C.E., but used at first only for Church business. Introduced in Italy in 7c., France (partially) in 8c. In England, first found in a charter of 680 C.E. Ordained for all ecclesiastical documents in England by the Council of Chelsea, July 27, 816.

The resistance to it might have come in part because Dionysius chose 754 A.U.C. as the birth year of Jesus, while many early Christians would have thought it was 750 A.U.C. (See John J. Bond, "Handy-Book of Rules and Tables for Verifying Dates With the Christian Era," 4th ed., London: George Bell & Sons, 1889.) There is a use of simple a for anno domini in an English document from c. 1400; A.C., for Anno Christi, also was common 17c.
a.k.a. Look up a.k.a. at Dictionary.com
also a k a, aka, initialism (acronym) for also known as; attested in legal documents from at least 1936.
a.m. Look up a.m. at Dictionary.com
also a.m., 1762 in reference to hours, an abbreviation of Latin ante meridiem "before noon" (q.v.). Synonymous with "morning" by 1776. AM as a type of radio wave broadcast, 1921, abbreviation of amplitude modulation (see amplitude). Affixed to a name, an abbreviation of artium magister "Master of Arts," an abbreviation preferable in a purely Latin idiom; British English prefered M.A. In some old chronologies, a.m. is anno mundi "year of the world."
A.P.R. Look up A.P.R. at Dictionary.com
also APR, abbreviation of annual percentage rate, attested from 1979, American English.
a.s.a.p. Look up a.s.a.p. at Dictionary.com
also asap, adverbial phrase pronounced either as a word (acronym) or as four letters (initialism), 1955, from initial letters of phrase as soon as possible; originally U.S. Army jargon.
A.V. Look up A.V. at Dictionary.com
abbreviation of Authorized Version (of the English Bible, 1611) attested from 1868.
aardvark (n.) Look up aardvark at Dictionary.com
also aard-vark, South African groundhog, 1833, from Afrikaans Dutch aardvark, literally "earth-pig" (it burrows), from aard "earth," from Proto-Germanic *ertho- (see earth) + vark "pig," which is from Proto-Germanic *farhaz- (source also of Old High German farah, German Ferkel "young pig, sucking pig," a diminutive form; Old English fearh; see farrow (n.)).
aardwolf (n.) Look up aardwolf at Dictionary.com
also aard-wolf, 1833, from Afrikaans Dutch aardwolf, literally "earth-wolf," from aard "earth" (see earth) + wolf "wolf" (see wolf (n.)).
Aaron Look up Aaron at Dictionary.com
masc. proper name, in the Old Testament the brother of Moses, from Hebrew Aharon, which is said to be probably of Egyptian origin. The Arabic form is Harun. Related: Aaronic. Aaron's beard as a popular name for various plants (including St. John's wort and a kind of dwarf evergreen) deemed to look hairy in some way is from 1540s. Aaron's rod is from 1834 in botany, 1849 in ornamentation; the reference is biblical (Exodus vii.19, etc.).
ab initio Look up ab initio at Dictionary.com
c. 1600, Latin, literally "from the beginning," from ab "from" (see ab-) + ablative of initium "entrance, beginning," which is from or related to the verb inire "to go into, enter upon, begin" (see initial).
ab- Look up ab- at Dictionary.com
word-forming element meaning "away, from, from off, down," denoting disjunction, separation, departure; from Latin ab-, ab (prep.) "off, away from" in reference to space or distance, also of time, from PIE root *apo- "off, away" (also the source of Greek apo "away from, from," Sanskrit apa "away from," Gothic af, English of, off; see apo-).

The Latin word also denoted "agency by; source, origin; relation to, in consequence of." Since classical times usually reduced to a- before -m-, -p-, or -v-; sometimes abs- before -c- or -t-.
aba (n.) Look up aba at Dictionary.com
outer garment of coarse, woolen stuff, of a type worn in Arabia and Syria, 1811, from Arabic. Also of the cloth it is made from (often goat or camel hair).
aback (adv.) Look up aback at Dictionary.com
c. 1200, a contraction of Old English on bæc "backward, behind, at or on the back;" see see a- (1) + back (n.). Now surviving mainly in taken aback, originally a nautical expression in reference to a vessel's square sails when a sudden change of wind flattens them back against the masts and stops the forward motion (1754). The figurative sense from this, "suddenly or unexpectedly checked or disappointed," is by 1840.
abacus (n.) Look up abacus at Dictionary.com
late 14c., "sand table for drawing, calculating, etc.," also "art of calculating with an abacus," from Latin abacus, from Greek abax (genitive abakos) "counting table," which is said to be from a Semitic source, Phoenician or Hebrew abaq "sand strewn on a surface for writing," literally "dust," from the Semitic root a-b-q "to fly off."

Originally a drawing board covered with dust or sand on which mathematical equations or calculations could be traced and erased. In reference to the other type of abacus, a counting frame with beads or balls strung on wires or rods, it is attested from 17c. or later in English. Both types were known in antiquity across Eurasia. Related: Abacist (late 14c.)
Abaddon Look up Abaddon at Dictionary.com
late 14c., used in Revelations ix.11 of "the angel of the bottomless pit," and by Milton of the pit itself, from Hebrew Abhaddon, literally "destruction," from abhadh "he perished." The Greek form was Apollyon.
abaft (adv.) Look up abaft at Dictionary.com
"in or further toward the back part (of a ship)," as opposed to forward, 1590s, from Middle English on baft (late 13c.) "back, behind, to the rear," from Old English on bæftan. For first element, see a- (1). The second component is itself a compound of be "by" (see by) and æftan "aft" (see aft). The word has been saved by the sailors (the stern being the "after" part of a vessel), the rest of the language having left it in Middle English.
abalienate (v.) Look up abalienate at Dictionary.com
in civil law, "transfer title of ownership to another," 1550s, from Latin abalienatus, past participle of abalienare "to remove, separate, alienate, make formal transfer of," literally "to convey away," from ab- "off, away from" (see ab-) + alienare "to separate" (see alienate). Related: Abalienated; abalienating.
abalienation (n.) Look up abalienation at Dictionary.com
"act of transferring title of ownership," 1650s, from Latin abalienationem (nominative abalienatio), in law, "transfer of property, sale," noun of action from past participle stem of abalienare "to separate, transfer the ownership of" (see abalienate).
abalone (n.) Look up abalone at Dictionary.com
type of large mollusk found on the California coastne shell, 1850, American English, from Spanish abulon, a loan-word from Rumsen (an extinct native language in the Costanoan family), aluan, said to mean "red abalone." Prized for its meat (once an important California export) and for the mother-of-pearl in its large shells (also called ear-shells).
abandon (v.) Look up abandon at Dictionary.com
late 14c., "to give up, surrender (oneself or something), give over utterly; to yield (oneself) utterly (to religion, fornication, etc.)," from Old French abandoner (12c.), from adverbial phrase à bandon "at will, at discretion," from à "at, to" (see ad-) + bandon "power, jurisdiction," from Latin bannum, "proclamation," from a Frankish word related to ban (v.).
Mettre sa forest à bandon was a feudal law phrase in the 13th cent. = mettre sa forêt à permission, i.e. to open it freely to any one for pasture or to cut wood in; hence the later sense of giving up one's rights for a time, letting go, leaving, abandoning. [Auguste Brachet, "An Etymological Dictionary of the French Language," transl. G.W. Kitchin, Oxford, 1878]
Etymologically, the word carries a sense of "put someone under someone else's control." Meaning "to give up absolutely" is from late 14c. Related: Abandoned; abandoning.
abandon (n.) Look up abandon at Dictionary.com
"a letting loose, surrender to natural impulses," 1822, from a sense in French abandon (see abandon (v.). Borrowed earlier (c. 1400) from French in a sense "(someone's) control;" and compare Middle English adverbial phrase at abandon, i.e. "recklessly," attested from late 14c.
abandoned (adj.) Look up abandoned at Dictionary.com
"self-devoted" to some purpose (usually evil), late 14c., past participle adjective from abandon (v.).
abandonment (n.) Look up abandonment at Dictionary.com
1610s, from French abandonnement, from abandonner (see abandon (v.)).
abase (v.) Look up abase at Dictionary.com
late 14c., abaishen, from Old French abaissier "diminish, make lower in value or status" (12c.), from Vulgar Latin *ad bassiare "bring lower," from ad- "to" (see ad-) + Late Latin bassus "thick, fat, low" (see base (adj.)). Form in English altered 16c. by influence of base (adj.), thus the word is an exception from the rule that Old French verbs with stem -iss- enter English as -ish. Related: Abased; abasing.
abasement (n.) Look up abasement at Dictionary.com
early 15c., "embarrassment, dread, fear," from abase + -ment. Sense of "action of lowering in price" is mid-15c.; "action of lowering in rank" is 1560s; "condition of being abased" is from 1610s.
abash (v.) Look up abash at Dictionary.com
"perplex, embarrass," early 15c., earlier "lose one's composure, be upset" (late 14c.), from Old French esbaiss-, present stem of esbaer "gape with astonishment," from es "out" (see ex-) + ba(y)er "to be open, gape," from Latin *batare "to yawn, gape," from root *bat, possibly imitative of yawning. Related: Abashed; abashing. Bashful is a 16c. derivative.
abate (v.) Look up abate at Dictionary.com
c. 1300, "put an end to;" early 14c., "to grow less, diminish in power or influence," from Old French abattre "beat down, cast down," from Vulgar Latin *abbatere, from Latin ad "to" (see ad-) + battuere "to beat" (see batter (v.)). Secondary sense of "to fell, slaughter" is in abatis and abattoir. Related: Abated; abating.
abatement (n.) Look up abatement at Dictionary.com
mid-14c., from Old French abatement, from abattre (see abate).