Online Etymology Dictionary

incombustible (adj.): "incapable of being burned or consumed by fire," late 15c., from Old French incombustible (14c.) or directly from Medieval Latin incombustibilis; see in- (1) + combustible. As a noun from 1807. Related: Combustibility.
incomparability (n.): c. 1500, incomparablete, "quality of being peerless," from incomparable + -ity.
inconstance (n.): late 14c., from Old French inconstance "inconstancy, instability" (13c.), from Latin inconstantia "inconstancy, fickleness," noun of quality from inconstans "changeable, inconsistent" (see inconstant). In English, inconstancy is now the usual word.
incontinence (n.): late 14c., "inability to restrain sexual desire, sexual immorality," later "inability to keep to a religious rule" (early 15c.), from Old French incontinence "lack of abstinence, unchastity" (12c.) or directly from Latin incontinentia "greediness; incontinence, inability to contain," noun of quality from incontinens "incontinent, immoderate, intemperate" (see incontinent). Meaning "inability to restrain bodily functions" is from 1754.
incontinency (n.): early 15c., "unchastity;" see incontinent + -cy.
incontinently (adv.): early 15c., "immediately, without delay, at once," from incontinent + -ly (2). From 1550s as "unchastely;" in reference to bodily discharges from 1847.
inconvenience (v.): 1650s, from inconvenience (n.). Related: Inconvenienced; inconveniencing.
inconveniently (adv.): mid-15c., "wrongfully," from inconvenient + -ly (2). Meaning "with trouble or discomfort" is from 1650s.
incorporation (n.): late 14c., incorporacioun, "act or process of combining substances; absorption of light or moisture," from Old French incorporacion or directly from Late Latin incorporationem (nominative incorporatio) "an embodying, embodiment," noun of action from past participle stem of incorporare "unite into one body" (see incorporate (v.)). Meaning "the formation of a corporate body (such as a guild) by the union of persons, forming an artificial person," is from early 15c.
Incorporation, n. The act of uniting several persons into one fiction called a corporation, in order that they may be no longer responsible for their actions. A, B and C are a corporation. A robs, B steals and C (it is necessary that there be one gentleman in the concern) cheats. It is a plundering, thieving, swindling corporation. But A, B and C, who have jointly determined and severally executed every crime of the corporation, are blameless. [Ambrose Bierce, 1885]
incorrigibility (n.): late 15c., from incorrigible + -ity.
indeclinable (adj.): late 14c., originally in grammar, from French indéclinable or directly from Latin indeclinabilis "unchangeable," also in grammar, from indeclinatus "unchanged, constant," from in- "not, opposite of" (see in- (1)) + declinatus, from declinare "to lower; avoid, deviate; bend from, inflect" (see decline (v.)). Related: Indeclinably.
indiction (n.): late 14c., "period of fifteen years," a chronological unit of the Roman calendar that continued in use through the Middle Ages, from Latin indictionem (nominative indictio), literally "declaration, appointment," noun of action from past participle stem of indicere "to declare publicly, proclaim, announce," from in- "in" (see in- (2)) + dicere "to speak, say, tell" (see diction).

Fixed by Constantine and reckoned from Sept. 1, 312. Originally for taxation purposes, it was "a common and convenient means for dating ordinary transactions" [Century Dictionary]. The name refers to the "proclamation," at the beginning of each period, of the valuation upon which real property would be taxed.
indifferently (adv.): late 14c., "alike, equally; indiscriminately;" c.1400, "unconcernedly, carelessly;" early 15c., "impartially, without preferring one to the other;" from indifferent + -ly (2).
indigestible (adj.): late 15c., from Late Latin indigestibilis or else a native formation from in- (1) "not, opposite of" + digestible; or else from Late Latin indigestibilis. Related: Indigestibility (1733).
indirectly (adv.): mid-15c., from indirect + -ly (2).
individual (n.): "single object or thing," c. 1600, from individual (adj.). Meaning "a single human being" (as opposed to a group, etc.) is from 1640s. Colloquial sense of "person" is attested from 1742. Latin individuum as a noun meant "an atom, indivisible particle," and in Middle English individuum was used in sense of "individual member of a species" (early 15c.).
indubitably (adv.): "unquestionably, without a doubt," late 15c., from indubitable + -ly (2).
inexpert (adj.): mid-15c., from in- (1) "not, opposite of" + expert (adj.), or else from Old French inexpert or directly from Latin inexpertus "without experience, unpracticed; untried, untested." Related: Inexpertly.
infective (adj.): "infectious, communicable by infection," late 14c., from Latin infectivus, from infect-, past participle stem of inficere "to tinge, dye; stain, spoil" (see infect).
inferior (n.): "person inferior to another in rank, etc.," early 15c., from inferior (adj.).
innocently (adv.): c. 1400, from innocent (adj.) + -ly (2).
insensibility (n.): late 14c., "absence of physical sensation, numbness," from Late Latin insensibilitas, from insensibilis "that cannot be felt" (see insensible). Meaning "quality of being imperceptible" is from 1630s. Meaning "absence of moral feeling, indifference" is from 1690s.
insensibly (adv.): "so as not to be felt or perceived," early 15c.; see insensible + -ly (2).
inspirer (n.): c. 1500, agent noun from inspire (v.). The Late Latin form, inspirator, is attested in English in 17c. in the Latin figurative sense but later was used literally as the name of a steam-engine part (1890). Inspirationist is "one who believes in the inspiration of the Scriptures (1846). As a fem. form of inspirer, inspiratrix (1819) has been used.
instant (adj.): mid-15c., "now, present, of the moment, current," from Old French instant "near, imminent, immediate, at hand; urgent, assiduous" (14c.) and directly from Medieval Latin instantem (nominative instans), in classical Latin "present, pressing, urgent," literally "standing near," present participle of instare "to urge, to stand near, be present (to urge one's case)," from in- "in" (see in- (2)) + stare "to stand," from PIE root *stā- "to stand" (see stet).

Sense of "immediate, done or occurring at once" is from 1590s. Of processed foods, by 1912; instant coffee is from 1915. Televised sports instant replay attested by 1965. Instant messaging attested by 1994. The word was used 18c.-19c. in dating of correspondence, meaning "the current month," often abbreviated inst. Thus 16th inst. means "sixteenth of the current month" (see ultimo).
instructor (n.): mid-15c., from Old French instructeur (14c.) and directly from Medieval Latin instructor "teacher" (in classical Latin, "preparer"), agent noun from instruere "arrange; inform, teach" (see instruct).
intellectuality (n.): mid-15c., "the part of the mind which understands; understanding, intellect;" from Old French intellectualité and directly from Late Latin intellectualitas, from Latin intellectualis "relating to the understanding" (see intellectual).
anti-imperialist (adj.): 1898, American English, in debates about the Spanish-American War, from anti- + imperialist. Related: Anti-imperialism.
hang in (v.): "persist through adversity," 1969, usually with there; see hang (v.) + in (adv.).
anti-intellectualism (n.): 1904, from anti- + intellectualism; or in some cases from anti-intellectual + -ism.
inadvertent (adj.): 1650s, "not properly attentive" (of persons), a back-formation from inadvertence. Meaning "unconscious, unintentional" (of actions) is from 1724.
inappropriate (adj.): 1791, from in- (1) "not, opposite of" + appropriate (adj.). Related: Inappropriately; inappropriateness. Unappropriate is from 1742.
inadequate (adj.): 1670s; see in- (1) "not, opposite of" + adequate. Related: Inadequately.
impudence (n.): late 14c., from Latin impudentia "shamelessness," noun of quality from impudens "shameless" (see impudent).
impulsive (adj.): early 15c., originally in reference to medicine that reduces swelling or humors, from Medieval Latin impulsivus, from Latin impuls-, past participle stem of impellere "strike against, push against" (see impel). Meaning "having the property of impelling" (of force, cause, energy, etc.) is from c. 1600. Of persons, "rash, characterized by impulses," from 1847, from impulse. Earlier, at least once, in reference to maniacs:
The impulsive insane are often irritable, restless and jealous. Sometimes they have delusions, and sometimes not. Their delusions frequently seem to have no connection with their outbreaks of violence. They are often the best and at the same time the most dangerous class of patients in the asylums. They have little of the charity of the world, are most likely to be punished for their offences, and yet have the least control over their conduct. ["Impulsive and Homicidal Insanity," Boston Medical and Surgical Journal," April 19, 1843]
-in (1): the adverb in attached to a verb as a word-forming element, by 1960, abstracted from sit-in, which is attested from 1941 in reference to protests and 1937 in reference to labor union actions (which probably was influenced by sit-down strike) but was popularized in reference to civil disobedience protests aimed at segregated lunch counters. As a word-forming element at first of other types of protests, extended by 1965 to any sort of communal gathering.
impassive (adj.): 1660s, "not feeling pain, insen" from assimilated form of in- "not, opposite of" (see in- (1)) + passive. Meaning "void of emotions, unmoved" is from 1690s. Related: Impassively; impassiveness (1640s).
impatient (adj.): late 14c., from Old French impacient "impatient" (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 "bearing, enduring" (see patience). Related: Impatiently.
immoral (adj.): 1650s, "not consistent with moral law or standards, ethically wrong," from assimilated form of in- (1) "not" + moral (adj.). In legal language it tends to mean merely "contrary to common good or reasonable order." Related: Immorally.
impede (v.): c. 1600, back-formation from impediment, or else from Latin impedire "impede, be in the way, hinder, detain," literally "to shackle the feet." Related: Impeded; impedes; impeding; impedient.
immigrant (n.): "one who immigrates," 1792, American English, perhaps based on French immigrant, from Latin immigrantem (nominative immigrans), present participle of immigrare "to remove, go into, move in" (see immigrate). Emigrant is older. First used in English in Jeremy Belknap's history of New Hampshire, and he generally is credited with having coined it.
There is another deviation from the strict letter of the English dictionaries; which is found extremely convenient in our discourses on population. From the verb migro are derived emigrate and IMMIGRATE; with the same propriety as from mergo are derived emerge and IMMERGE. Accordingly the verb IMMIGRATE and the nouns IMMIGRANT and IMMIGRATION are used without scruple in some parts of this volume. [Preface to vol. III of "The History of New Hampshire," Belknap, 1792]
As an adjective from 1805.
immigration (n.): 1650s, noun of action from immigrate. As "immigrants collectively," from 1852. As short for "immigration authorities," from 1966.
immensely (adv.): 1650s, from immense + -ly (2).
implications (n.): see implication.
implicate (v.): early 15c., "to convey (truth) in a fable," from Latin implicatus, past participle of implicare "to involve, entwine, entangle, embrace" (see implication). From c. 1600 as "intertwine, wreathe." Meaning "involve (someone) in a crime, charge, etc.; show (someone) to be involved" is from 1797. Related: Implicated; implicating.
immediately (adv.): "without intervening time or space, directly," early 15c., from immediate + -ly (2).
imbecile (adj.): 1540s, imbecille "weak, feeble" (especially in reference to the body), from Middle French imbecile "weak, feeble" (15c.), from Latin imbecillus "weak, feeble" (see imbecility). Sense shifted to mental weakness or incapacity from mid-18c. (compare frail, which in provincial English also could mean "mentally weak"). As a noun, "feeble-minded person," it is attested from 1802. Traditionally an adult with a mental age of roughly 6 to 9 (above an idiot but beneath a moron).
imagery (n.): mid-14c., "piece of sculpture, carved figures," from Old French imagerie "figure" (13c.), from image "likeness, figure, drawing, portrait" (see image (n.)). Rhetorical meaning "ornate description, exhibition of images to the mind" (in poetry, etc.) is from 1580s.
impressed (adj.): early 15c., "pressed or forced upon" (the mind), past participle adjective from impress (v.).
importunate (adj.): 1520s, from importune + -ate (1), or else from Medieval Latin importunatus, past participle of importunari "to make oneself troublesome." Related: Importunately (mid-15c.). Earlier adjective was importune (c. 1400).