iamb (n.)
1842, from French iambe (16c.), from Latin iambus, from Greek iambos (see iambic). Iambus itself was used in English in this sense in 1580s.
iambic
1570s (n.); 1580s (adj.), from Latin iambicus, from Greek iambikos, from iambos "metrical foot of one unaccented followed by one accented syllable," from iaptein "to assail" (in words), literally "to put forth." The meter of invective and lampoon in classical Greek from the time it was used for such by Archilochos, 7c. B.C.E.
Ian
masc. proper name, Scottish form of John.
iatro-
word-forming element meaning "physician, medicine, healing," from Greek iatro-, comb. form of iatros "healer, physician" (see -iatric).
iatrogenic (adj.)
1920, from iatro- + -genic.
Iberian
c.1600 (n.); 1610s (adj.), from Latin Iberia, ancient name of the Spanish peninsula, from Greek Iberes "Celtic people of Spain;" also the name given to an Asiatic people near the Caucasus. Of unknown origin in both uses, but the word as applied in Spain is believed to be related to the River Ebro. The earliest English reference is to the Caucasians; in reference to Spain and Portugal it dates from 1610s.
ibex (n.)
c.1600, from Latin ibex "wild goat of the Alps and Apennines," from a pre-Latin Alpine language. The German steinbock.
ibid.
also ibid, 1660s, abbreviation of Latin ibidem "in the same place," from ibi "there," pronomial adverb of place, + demonstrative suffix -dem.
ibis (n.)
stork-like bird, late 14c., from Greek ibis, from Egyptian hab, a sacred bird of Egypt.
IBM
also (in early use) I.B.M., initialism (acronym) attested by 1921 from International Business Machines Co., name in use from 1918.
ibogaine (n.)
nerve stimulant, 1901, from French ibogaine, from iboga, Congolese name of the shrub from which the chemical is extracted, + chemical suffix -ine (2).
Icarus
son of Daedalus in Greek mythology; he flew too high on artificial wings and so plunged to his death. Used allusively from 1580s. The name is of unknown origin.
ICBM (n.)
1955, initialism (acronym) for Inter-Continental Ballistic Missile.
ice (n.)
Old English is "ice" (also the name of the rune for -i-), from Proto-Germanic *isa- (cognates: Old Norse iss, Old Frisian is, Dutch ijs, German Eis), with no certain cognates beyond Germanic, though possible relatives are Avestan aexa- "frost, ice," isu- "frosty, icy;" Afghan asai "frost." Slang meaning "diamonds" is attested from 1906.

Ice cube attested from 1904. Ice age attested from 1832. To break the ice "to make the first opening to any attempt" is from 1580s, metaphoric of making passages for boats by breaking up river ice though in modern use usually with implications of "cold reserve."
ice (v.)
c.1400, ysen, "cover with ice," from ice (n.). Related: Iced; icing.
ice cream (n.)
1744, earlier iced cream (1680s), from ice (n.) + cream (n.).
Ice-Capade (n.)
1941, originally a film title, from ice (n.) + play on escapade.
ice-cold (adj.)
Old English is-calde; see ice (n.) + cold (adj.).
ice-skate (v.)
1690s, from ice (n.) + skate (n.2). The verb usually was simply skate until the advent of roller-skating mid-18c. made distinction necessary.
ice-water (n.)
1722, from ice (n.) + water (n.1).
iceberg (n.)
1774, partial loan-translation of Dutch ijsberg, literally "ice mountain," from ijs "ice" (see ice (n.)) + berg "mountain" (see barrow (n.2)). An earlier term was sea-hill (1690s). Phrase tip of the iceberg, in a figurative sense, first recorded 1962. Iceberg lettuce attested from 1893.
icebox (n.)
also ice-box, 1839, from ice (n.) + box (n.).
iceman (n.)
1844, from ice (n.) + man (n.).
ichneumon (n.)
1570s, originally a weasel-like animal in Egypt, Latinized from Greek ikhneumon, literally "searcher, tracker," perhaps because it hunts crocodile eggs, from ikhneuein "hunt for, track," from ikhnos "a track, footstep, trace, clue," of unknown origin. Used by Aristotle for a species of wasp that hunts spiders (a sense in English from 1650s).
ichor (n.)
1630s, from Greek ikhor, of unknown origin, possibly from a non-Indo-European language. The fluid that serves for blood in the veins of the gods. Related: Ichorous.
ichthyology (n.)
1640s, Modern Latin, from Greek ikhthys "fish" + -ology. Related: Ichthyologist.
Ichthyosaur (n.)
extinct reptile, 1830, Modern Latin, from Greek ikhthys "fish" + sauros "lizard" (see -saurus).
ichthyosis (n.)
1815, Modern Latin, from Greek ikhthys "fish" + -osis.
icicle (n.)
early 14c., isykle, from is "ice" + ikel "icicle," from Old English gicel "icicle, ice" (rel. to cylegicel "cold ice"), from Proto-Germanic *jekilaz (cognates: Old Norse jaki "piece of ice," diminutive jökull "icicle, ice, glacier;" Old High German ihilla "icicle"), from PIE *yeg- "ice." Dialectal ickle "icicle" survived into 20c.
icing (n.)
1769 in the confectionary sense, verbal noun of ice (v.). Earlier in this sense was simple ice (1723). Meaning "process of becoming covered with ice" is from 1881.
Icknield Way
prehistoric trackway from Norfolk to Dorset, Old English Icenhylte (903), of unknown meaning and origin. Name transferred 12c. to the Roman road from Burton on the Water to Templeborough.
icky (adj.)
1935, American English, probably from icky-boo (c.1920) "sickly, nauseated," probably baby talk elaboration of sick. Originally a swing lover's term for more sentimental jazz music; in general use from 1938.
icon (n.)
also ikon, 1570s, "image, figure, representation," from Late Latin icon, from Greek eikon "likeness, image, portrait," related to eikenai "be like, look like," of unknown origin. Eastern Church sense is attested from 1833. Computing sense first recorded 1982.
iconic (adj.)
1650s, from Late Latin iconicus, from Greek eikonikos "pertaining to an image," from eikon (see icon).
iconoclasm (n.)
1797 in reference to breaking of idols; 1858 in reference to beliefs, institutions, etc.; see iconoclast + -ism.
iconoclast (n.)
"breaker or destroyer of images," 1590s, from French iconoclaste and directly from Medieval Latin iconoclastes, from Late Greek eikonoklastes, from eikon (genitive eikonos) "image" + klastes "breaker," from klas- past tense stem of klan "to break" (see clastic). Originally those in the Eastern Church in 8c. and 9c. whose mobs of followers destroyed icons and other religious objects on the grounds that they were idols. Applied to 16c.-17c. Protestants in Netherlands who vandalized former Catholic churches on similar grounds. Extended sense of "one who attacks orthodox beliefs or institutions" is first attested 1842.
iconoclastic (adj.)
1640s; see iconoclast + -ic.
iconography (n.)
1620s, from Medieval Latin iconographia, from Greek eikonographia "sketch, description," from eikon (see icon) + -graphia (see -graphy). Related: Iconographic.
icosahedron (n.)
1560s, from Greek eikosahedron, neuter of eikosahedros, from eikosi "twenty" + -hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit" (see sedentary). Greek eikosi is from PIE *wikmti- "twenty," from *wi- "in half," hence "two" + (d)kmti-, from root *dekm- "ten" (see ten).
icteric (adj.)
c.1600, from Latin ictericus, from Greek ikterikos "jaundiced," from ikteros (see icterus). Related: Icterical.
icterus (n.)
1706, medical Latin, from Greek ikteros "jaundice," also the name of a yellowish bird the sight of which was supposed, by sympathetic magic, to cure jaundice. As a zoological genus, from 1713.
ictus (n.)
verse stress, 1752, from Latin ictus "a blow, stroke, thrust," of voices "a beat, impulse, stress," from icere "to strike, hit," related to iacere "to throw" (see jet (v.)).
icy (adj.)
Old English isig; see ice (n.) + -y (2). Modern use is said to be a late Middle English re-formation. Figurative use from 1590s. Related: Icily; iciness.
id (n.)
1924, in Joan Riviere's translation of Freud's "Das Ich und das Es" (1923), from Latin id "it" (translation of German es "it" in Freud's title), used in psychoanalytical theory to denote the unconscious instinctual force. Latin id is from PIE pronomial stem *i- (see yon).
id est
Latin, literally "that is (to say)."
Ida
fem. proper name, from Medieval Latin, from Old High German Ida, perhaps related to Old Norse "work."
Idaho
c.1860, as a place name, originally applied to part of what is now eastern Colorado (Idaho Territory organized 1863; admitted as a state 1890); from Kiowa-Apache (Athabaskan) idaahe "enemy," a name applied by them to the Comanches.
idea (n.)
late 14c., "archetype of a thing in the mind of God; Platonic `idea,'" from Latin idea "idea," and in Platonic philosophy "archetype," from Greek idea "ideal prototype," literally "the look of a thing (as opposed to the reality); form; kind, sort, nature," from idein "to see," from PIE *wid-es-ya-, suffixed form of root *weid- "to see" (see vision). Sense of "result of thinking" first recorded 1640s.
Men of one idea, like a hen with one chicken, and that a duckling. [Thoreau, "Walden"]
Idée fixe (1836) is from French, literally "fixed idea."
ideal (adj.)
early 15c., "pertaining to an archetype or model," from Late Latin idealis "existing in idea," from Latin idea in the Platonic sense (see idea). Sense of "perfect" first recorded 1610s.
ideal (n.)
"perfect person or thing," 1796, in a translation of Kant, from ideal (adj.).