Online Etymology Dictionary

impacted (adj.): 1680s, "pressed closely in," past-participle adjective from impact (v.). Of teeth from 1859.
imparity (n.): 1560s, from Late Latin imperitas, from assimilated form of in- "not, opposite of" (see in- (1)) + paritas "equality" (see parity). Rare or obsolete.
impanel (v.): "to fit with panels," 1570s; see im- "in" + panel (n.). Related: Impanelled. Also empanel.
impartible (adj.): late 14c. as "indivisible, incapable of being parted," from Medieval Latin impartibilis; see im- "not, opposite of" + part (v.). From 1630s as "capable of being imparted," from impart (v.) + -ible. Now little used in either sense.
impatiens (n.): type of flowering plant, from Latin impatiens "impatient" (see impatient). So called in reference to the valves of the seed pods, which discharge forcibly at a slight touch.
imperception (n.): "want of perception," 1620s, from assimilated form of in- (1) "not, opposite of" + perception.
imperceptive (adj.): "not perceiving," 1660s, from assimilated form of in- (1) "not, opposite of" + perceptive.
imperturbed (adj.): 1721, from assimilated form of in- (1) "not" + perturbed. Related: Imperturbedly.
impersuasible (adj.): 1570s, from assimilated form of in- (1) "not, opposite of" + persuasible (see persuadable).
implex (adj.): "intricate, complicated," 1710, from Latin implexus "interwoven, entwined," past participle of implectere. Used by 18c. critics in reference to plots.
implicative (adj.): "tending to implicate," c. 1600, from implicate + -ive. Related: Implicatively (1570s).
implied (adj.): "intended but not expressed," 1520s, past participle adjective from imply (v.). Implied powers in a constitutional sense is attested from 1784.
implete (v.): "to fill, pervade," 1862, from Latin impletus, past participle of implere "to fill, fill up" (see implement (n.)). OED says U.S. Related: Impleted; impleting.
impletion (n.): "action of filling," 1580s, from Late Latin impletionem, noun of action from stem of implere "to fill, fill up" (see implement (n.)).
implosive (adj.): 1876, originally in linguistics, probably from implode on the model of explosive; implosive is attested in French and German from 1860s.
importer (n.): 1700, agent noun from import (v.).
impossibilism (n.): "belief in social reforms (or other ideas) that could not practically be attained or accomplished," 1885, from impossible + -ism. Related: Impossibilist.
impotable (adj.): "undrinkable," c.1600, from assimilated form of in- (1) "not" + potable, or else from Late Latin impotabilis.
impersuadable (adj.): 1763, from assimilated form of in- (1) "not, opposite of" + persuadable. [Earliest date in OED 2nd ed. print is a typo.]
impracticality (n.): 1843; see impractical + -ity.
impress (v.2): "levy for military service," 1590s, from assimilated form of in- (2) "into, in" + press (v.2). Related: Impressed; impressing.
impressible (adj.): "capable of receiving impression," 1620s, from impress (v.1) + -able. Related: Impressibly; impressibility.
impressable (adj.): "liable to be impressed into public service," 1865, from impress (v.2) + -able. Earlier it was used in the sense "capable of receiving impression" and "impressionable." Related: Impressability.
imprint (n.): mid-15c., emprente "an imprint or mark, impression made by printing or stamping," from Old French empreinte "mark, impression, imprint" (see imprint (v.)). Meaning "publication information of a book" (1790) is directly from the verb.
improbity (n.): "want of integrity," 1590s, from Latin improbitas "badness, dishonesty," from assimilated form of in- "not" (see in- (1)) + probitas "uprightness, honesty," from probus "worthy, good" (see prove).
improvable (adj.): 1640s, from improve (v.) + -able.
Impuritan (n.): "one who is not a Puritan," 1610s, a hostile coinage of the Puritans, from im- "not, opposite of" + Puritan, perhaps also with suggestion of impure.
in (adj.): "that is within, internal," 1590s, from in (adv.). Sense of "holding power" (the in party) first recorded c. 1600; that of "exclusive" (the in-crowd, an in-joke) is from 1907 (in-group); that of "stylish, fashionable" (the in thing) is from 1960.
impregnability (n.): 1755, from impregnable + -ity.
ironmonger (n.): also iron-monger, "dealer in iron-ware," mid-14c. (mid-12c. as a surname), from iron (n.) + monger (n.). Early forms also include ismongere, irenmanger, iremonger. A street named Ysmongeres lane is attested in London from c. 1215. Related: Ironmongery.
in forma pauperis: legal Latin, literally "in the form of a poor person" (thus exempt from certain court fees, etc.), 1590s; see form (n.) + pauper (n.).
in-patient (n.): also inpatient, 1760, "person who stays in a hospital for treatment," from in (prep.) + patient (n.). As an adjective by 1890.
in fieri: legal Latin, "in the process of being done," from fieri "to come into being, become," used as passive of facere "to make, do" (see factitious).
impromptitude (n.): 1848, probably from French impromptitude, from assimilated form of in- "not, opposite of" (see in- (1)) + promptitude (see prompt (adj.)).
imprevisible (adj.): "that cannot be foreseen," 1855, from assimilated form of in- "not, opposite of" (see in- (1)) + previsible (see pre- + visible). Related: Imprevision; imprevisibility.
impoliteness (n.): 1670s, from impolite + -ness.
inappetence (n.): "failure of appetite," 1690s, from French inappétence (16c.), from assimilated form of in- "not, opposite of" (see in- (1)) + appétence "desire" (for food); see appetence. Related: Inappetency (1610s).
inappreciable (adj.): 1773, "too inconsiderable to matter;" 1787, "that cannot be sufficiently appreciated," from in- (1) "not, opposite of" + appreciable. Perhaps modeled on French inappreciable. Related: Inappreciably.
inapprehensible (adj.): 1640s, from in- (1) "not, opposite of" + apprehensible.
inboard (adv.): "within the hull or interior of a ship," 1830, from in (adv.) + board (n.2).
incendiary (adj.): mid-15c., "capable of being used to set fires," from Latin incendiarius "causing a fire," from incendium "a burning, a fire, conflagration," from incendere "set on fire, light up with fire, brighten," figuratively, "incite, rouse, excite, enrage," from in- "into, in, on, upon" (see in- (2)) + candere "to shine, glow, be on fire" (see candle).

Figurative sense of "enflaming passions" is from 1610s in English. Meaning "relating to criminal burning" is from 1610s. Military use, of bombs, shells, etc., attested from 1871. The obsolete poetic verb incend is attested from c. 1500.
incensed (adj.): "full of wrath, inflamed with anger," 1590s, past-participle adjective from incense (v.1). Earlier it was used in heraldry, in reference to fire-breathing animals (1570s). Distinguished in pronunciation from incensed "perfumed witrh incense" (1610s), from incense (v.2).
incentive (adj.): c. 1600, "provocative, exciting, encouraging," from Late Latin incentivus "inciting" (see incentive (n.)). In reference to a system of rewards meant to encourage harder work, first attested 1943 in jargon of the U.S. war economy.
inchoative (adj.): 1630s, "indicating beginning or inception;" see inchoate + -ive. Especially in grammar, of verbs, "denoting the beginning of action, inceptive," 1660s.
inchmeal (adv.): "by inches, inch by inch," 1580s, from inch (n.1) + Middle English meal "fixed time, period of time, occasion" (see meal (n.1)).
incivism (n.): "want of good citizenship," in English often with a menacing sense, a word from the French Revolution, 1794, from French incivisme; see in- (1) "not" + civic + -ism.
The words civisme and incivisme came into use during the first French revolution, when an appearance of active devotion to the existing government was the great test of good citizenship, and incivism was regarded a crime. [Century Dictionary]
inclose (v.): alternative form of enclose (q.v.).
inclosure (n.): variant of enclosure preserved in some legal uses. Related: Inclosure.
inclined (adj.): c. 1300, "having a mental tendency;" 1540s, "having a physical slope," past-participle adjective from incline (v.).
inclusive (adj.): "characterized by including a great deal, leaving little out," c. 1600, from Medieval Latin inclusivus (see inclusive (adv.)). The Middle English adjective was incluse "confined, shut in" (late 14c.). Related: Inclusively; inclusiveness.