immutable (adj.) Look up immutable at Dictionary.com
early 15c., from Old French immutable and directly from Latin immutabilis "unchangeable," from assimilated form of in- "not, opposite of" (see in- (1)) + mutabilis "changeable," from mutare "to change" (see mutable). Related: Immutably.
imp (n.) Look up imp at Dictionary.com
Old English impe, impa "young shoot, graft," from impian "to graft," probably an early West Germanic borrowing from Vulgar Latin *imptus, from Late Latin impotus "implanted," from Greek emphytos, verbal adjective formed from emphyein "implant," from em- "in" + phyein "to plant" (see physic).

Sense of "child, offspring" (late 14c.) came from transfer of word from plants to people, with notion of "newness" preserved. Modern meaning "little devil" (1580s) is from common use in pejorative phrases like imp of Satan.
Suche appereth as aungelles, but in very dede they be ymps of serpentes. ["The Pilgrimage of Perfection," 1526]
impact (v.) Look up impact at Dictionary.com
c.1600, "press closely into something," from Latin impactus, past participle of impingere "to push into, dash against, thrust at" (see impinge). Originally sense preserved in impacted teeth (1876). Sense of "strike forcefully against something" first recorded 1916. Figurative sense of "have a forceful effect on" is from 1935. Related: Impacting.
impact (n.) Look up impact at Dictionary.com
1781, "collision," from impact (v.). Figurative sense of "forceful impression" is from 1817 (Coleridge).
impactful (adj.) Look up impactful at Dictionary.com
1968, from impact + -ful. Related: Impactfully; impactfulness.
impaction (n.) Look up impaction at Dictionary.com
1739, from Latin impactionem (nominative impactio) "a striking against," noun of action from past participle stem of impingere (see impinge).
impair (v.) Look up impair at Dictionary.com
late 14c., earlier ampayre, apeyre (c.1300), from Old French empeirier (Modern French empirer), from Vulgar Latin *impeiorare "make worse," from assimilated form of in- "into, in" (see in- (2)) + Late Latin peiorare "make worse" (see pejorative). In reference to driving under the influence of alcohol, first recorded 1951 in Canadian English. Related: Impaired; impairing.
impairment (n.) Look up impairment at Dictionary.com
mid-14c., emparement, from Old French empeirement, from empeirier (see impair). Re-Latinized spelling is from 1610s.
impala (n.) Look up impala at Dictionary.com
1875, from Zulu im-pala "gazelle."
impale (v.) Look up impale at Dictionary.com
1520s, "to enclose with stakes, fence in," from Middle French empaler and directly from Medieval Latin impalare "to push onto a stake," from assimilated form of in- "into, in" (see in- (2)) + Latin palus "a stake, prop, stay; wooden post, pole," from PIE *pak-slo-, from root *pag-/*pak- "to fasten" (see pact). Sense of "pierce with a pointed stake" (as torture or punishment) first recorded 1610s. Related: Impaled; impaling.
impalement (n.) Look up impalement at Dictionary.com
1590s, from French empalement, from empaler (see impale).
impalpable (adj.) Look up impalpable at Dictionary.com
c.1500, from French impalpable, from Medieval Latin impalpabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + palpabilis (see palpable). Figurative use from 1774. Related: Impalpably; impalpability.
impanate (adj.) Look up impanate at Dictionary.com
"present in the (consecrated) bread," 1540s, from Church Latin impanatus, past participle of impanare "to embody in bread," from assmiliated form of in- "in, into" (see in- (2)) + panis "bread" (see food).
impart (v.) Look up impart at Dictionary.com
early 15c., "to give a part of (one's possessions); late 15c., "to share, take part," from Old French impartir (14c.), from Late Latin impartire (also impertire) "to share in, divide with another, communicate," from assimilated form of in- "into, in" (see in- (2)) + partire "to divide, part" (see part (v.)). Related: Imparted; imparting.
impartial (adj.) Look up impartial at Dictionary.com
formed in English 1590s from assimilated form of in- (1) "not, opposite of" + partial. First recorded in "Richard II."
impartiality (n.) Look up impartiality at Dictionary.com
1610s; see impartial + -ity.
impassable (adj.) Look up impassable at Dictionary.com
"that cannot be passed," 1560s, from im- + passable.
impasse (n.) Look up impasse at Dictionary.com
1851, "blind alley," from French impasse "impassable road, blind alley, impasse," from assimilated form of in- "not, opposite of" (see in- (1)) + Middle French passe "a passing," from passer "to pass" (see pass (v.)). Supposedly coined by Voltaire as a euphemism for cul de sac. Figurative use also from 1851.
impassible (adj.) Look up impassible at Dictionary.com
"incapable of feeling pain, exempt from suffering," mid-14c., from Old French impassible (13c.), from Church Latin impassibilis "incapable of passion," from assimilated form of in- "not, opposite of" (see in- (1)) + passibilis, from passio "suffering" (see passion). Related: Impassibility.
impassion (v.) Look up impassion at Dictionary.com
1590s, from Italian impassionare "to fill with passion," from im- "in, into" (see im-) + passione "passion," from Latin passionem (see passion). Related: Impassioned.
impassionate (adj.) Look up impassionate at Dictionary.com
"free from passion," 1620s, from in- (1) "not" + passionate. Related: Impassionately.
impassioned (adj.) Look up impassioned at Dictionary.com
c.1600, past participle adjective from impassion.
impassive (adj.) Look up impassive at Dictionary.com
1660s, "not feeling pain," from assimilated form of in- "not, opposite of" (see in- (1)) + passive. Meaning "void of emotions" is from 1690s. Related: Impassively; impassiveness (1640s).
impassivity (n.) Look up impassivity at Dictionary.com
1794, from impassive + -ity.
impasto (n.) Look up impasto at Dictionary.com
laying on of colors thickly," 1784, from Italian impasto, noun of action from impastare "to raise paste; to put in paste," from assimilated form of in- "into, in" (see in- (2)) + pasta "paste" (see pasta).
impatience (n.) Look up impatience at Dictionary.com
c.1200, from Old French impacience (Modern French impatience) and directly from Latin impatientia, from impatiens (see impatient).
impatient (adj.) Look up impatient at Dictionary.com
late 14c., from Old French impacient (Modern French impatient), from Latin impatientem (nominative impatiens) "that cannot bear, intolerant, impatient," from assimilated form of in- "not, opposite of" (see in- (1)) + patiens (see patience). Related: Impatiently.
impeach (v.) Look up impeach at Dictionary.com
late 14c., "to impede, hinder, prevent," from Anglo-French empecher, Old French empeechier "hinder" (12c., Modern French empêcher), from Late Latin impedicare "to fetter, catch, entangle," from assimilated form of in- "into, in" (see in- (2)) + Latin pedica "shackle," from pes (genitive pedis) "foot." Sense of "accuse a public officer of misconduct" first recorded 1560s, perhaps via confusion with Latin impetere "attack, accuse." Related: Impeached; impeaching.
impeachable (adj.) Look up impeachable at Dictionary.com
c.1500, from impeach + -able. Related: impeachably; impeachability.
impeachment (n.) Look up impeachment at Dictionary.com
late 14c., enpechement "accusation, charge," from Old French empechement, from empeechier (see impeach). As a judicial proceeding against a public official, from 1640s.
impeccable (adj.) Look up impeccable at Dictionary.com
1530s, "not capable of sin," from Middle French impeccable (15c.) or directly from Late Latin impeccabilis "not liable to sin," from assimilated form of in- "not, opposite of" (see in- (1)) + pecare "to sin," of unknown origin. Meaning "faultless" is from 1610s. Related: Impeccably.
impecunious (adj.) Look up impecunious at Dictionary.com
"lacking in money," 1590s, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin pecuniosus "rich," from pecunia "money, property" (see pecuniary). Related: Impecuniously; impecuniosity.
impedance (n.) Look up impedance at Dictionary.com
1886, from impede + -ance.
impede (v.) Look up impede at Dictionary.com
c.1600, back-formation from impediment, or else from Latin impedire "impede, be in the way, hinder, detain," literally "to shackle the feet" (see impediment). Related: Impeded; impedes; impeding.
impediment (n.) Look up impediment at Dictionary.com
c.1400, from Latin impedimentem "hindrance," from impedire "impede," literally "to shackle the feet," from assimilated form of in- "into, in" (see in- (2)) + pes (genitive pedis) "foot" (see foot (n.)).
impedimenta (n.) Look up impedimenta at Dictionary.com
"traveling equipment," c.1600, from Latin impedimenta "luggage, baggage," literally "that by which one is impeded;" plural of impedimentum (see impediment).
impel (v.) Look up impel at Dictionary.com
early 15c., from Latin impellere "to push, strike against, drive forward, urge on," from assimilated form of in- "into, in, on, upon" (see in- (2)) + pellere "to push, drive" (see pulse (n.1)). Related: Impelled; impelling.
impeller (n.) Look up impeller at Dictionary.com
1680s, agent noun from impel (v.). As a machine part from 1890.
impend (v.) Look up impend at Dictionary.com
1590s, from figurative use of Latin impendere "to hang over, to be imminent," from assimilated form of in- "into, in, on, upon" (see in- (2)) + pendere "hang" (see pendant). Related: Impended; impending.
impendent Look up impendent at Dictionary.com
1590s, from Latin impendens "impending," present participle of impendere (see impend).
impenetrable (adj.) Look up impenetrable at Dictionary.com
mid-15c., from Middle French impenetrable, from Latin impenetrabilis "that cannot be penetrated," from assimilated form of in- "not, opposite of" (see in- (1)) + penetrabilis "penetrable" (see penetrate). Related: Impenetrably; impenetrability.
impenitence (n.) Look up impenitence at Dictionary.com
1620s, from Latin impaenitentia, from impaenitens (see impenitent). Impenitency is from 1560s.
impenitent (adj.) Look up impenitent at Dictionary.com
early 15c., from Latin impaenitentem, from assimilated form of in- "not, opposite of" (see in- (1)) + paenitens (see penitence).
imperative (adj.) Look up imperative at Dictionary.com
1520s, from Late Latin imperativus "pertaining to a command," from imperatus "commanded," past participle of imperare "to command, to requisition," from assimilated form of in- "into, in" (see in- (2)) + parare "prepare" (see pare).
imperative (n.) Look up imperative at Dictionary.com
mid-15c., in grammar; later "something imperative" (c.1600), from Old French imperatif and directly from Late Latin imperativus (see imperative (adj.)).
imperator (n.) Look up imperator at Dictionary.com
"commander-in-chief," Latin agent noun from stem of imperare "to command" (see imperative). In the Roman republic, a commander; in the Roman Empire, the emperor.
imperceptibility (n.) Look up imperceptibility at Dictionary.com
1670s, from imperceptible + -ity.
imperceptible (adj.) Look up imperceptible at Dictionary.com
early 15c., from French imperceptible (early 15c.), from Medieval Latin imperceptibilis, from assimilated form of in- "not, opposite of" (see in- (1)) + perceptibilis (see perceptible). Related: Imperceptibly. OED marks imperceivable as "Now rare."
imperfect (adj.) Look up imperfect at Dictionary.com
mid-14c., imperfite, from Old French imparfait, from Latin imperfectus "unfinished, incomplete," from assimilated form of in- "not, opposite of" (see in- (1)) + perfectus (see perfect). Replaced mid-16c. by the Latin form. Related: Imperfectly.
imperfection (n.) Look up imperfection at Dictionary.com
late 14c., from Old French imperfeccion (12c.) and directly from Late Latin imperfectionem (nominative imperfectio), from imperfectus (see imperfect).