Online Etymology Dictionary

impressionable (adj.): "susceptible to (mental) impressions," 1827, from French impressionable (earliest English examples are in French translations and settings); see impression + -able. Related: Impressionability (1831). Earlier was impressible (1620s).
impressive (adj.): 1590s, "capable of being easily impressed" (a sense now rare or obsolete), from impress (v.1) + -ive. Meaning "capable of making an impression on the mind or senses, tending to excite attention and feeling" is from 1775. Related: Impressively; impressiveness.
idiosyncratic (n.): 1756, from idiosyncrasy + -ic. Earlier in same sense was idiosyncratical (1640s). Related: Idiosyncratically.
idyllic (adj.): "full of natural, simple charm," 1831, literally "suitable for an idyll" from French idyllique or else from idyll + -ic. In late 18c. it meant "pertaining to an idyll."
ignominy (n.): 1530s, back-formation from ignominious or else from Middle French ignominie (15c.), from Latin ignominia "disgrace, dishonor" (see ignominious). Also sometimes shortened to ignomy.
ignorance (n.): c. 1200, "lack of wisdom or knowledge," from Old French ignorance (12c.), from Latin ignorantia "want of knowledge" (see ignorant). Ignoration (1832) has been used in the sense "act of ignoring."
imagism (n.): name of a movement in poetry that sought clarity of expression through use of precise visual images, "hard light, clear edges" [Pound], coined 1912 by Ezra Pound; see image (n.) + -ism. Related: Imagist.
—Say it, no ideas but in things—
nothing but the blank faces of the houses
and cylindrical trees
bent, forked by preconception and accident—
split, furrowed, creased, mottled, stained—
secret—into the body of the light!

[William Carlos Williams, from "Paterson"]
imperialism (n.): 1826, "advocacy of empire, devotion to imperial interests," originally in a Napoleonic context, also of Rome and of British foreign policy; from imperial + -ism. At times in British usage (and briefly in U.S.) with a neutral or positive sense relating to national interests or the spread of the benefits of Western civilization, but from the begining usually more or less a term of reproach. General sense of "one country's rule over another," first recorded 1878. Picked up disparagingly in Communist jargon by 1918.
It is the old story of 1798, when French republicanism sick of its own folly and misdeeds, became metamorphosed into imperialism, and consoled itself for its incapacity to found domestic freedom by putting an iron yoke upon Europe, and covering it with blood and battle-fields. [Francis Lloyd, "St. James's Magazine," January 1842]
imperialist (n.): c. 1600, "an adherent of an emperor or the imperial cause," such as the emperor of Germany (in the Thirty Years War), France, China, etc., probably modeled on French impérialiste (early 16c.); from imperial + -ist. The shift in meaning to "advocate of imperialism" (1893) came via the British Empire, which involved a worldwide colonial system. See imperialism. As a term of abuse in communist circles, attested by 1918. As an adjective by 1816.
Easter Island: so called because it was discovered by Dutch navigator Jakob Roggeveen on April 2, 1722, which was Easter Monday. It earlier had been visited by English pirate Edward Davis (1695), but he neglected to name it. The native Polynesian name is Mata-kite-ran "Eyes that Watch the Stars."
beau-ideal (n.): 1801, from French beau idéal "the ideal beauty, beautifulness as an abstract ideal," in which beau is the subject, but as English usually puts the adjective first, the sense has shifted in English toward "perfect type or model."
incisive (adj.): early 15c., inscisif, "slashing, cutting with a sharp edge," from Old French incisif (medical) "invasive, effective," and directly from Medieval Latin incisivus, from Latin incis-, past participle stem of incidere "to cut into" (see incision). Originally literal; figurative sense of "mentally acute, sharply and clearly expressive" first recorded 1850 as a borrowing from French. Related: Incisively; incisiveness.
inconsequential (adj.): 1620s, "characterized by inconsequence;" 1782, "not worth noticing;" see inconsequent + -al (1). Related: Inconsequentially.
inclination (n.): "condition of being mentally disposed" (to do something), late 14c., from Middle French inclination (14c.) and directly from Latin inclinationem (nominative inclinatio) "a leaning, bending," figuratively "tendency, bias, favor," noun of action from past participle stem of inclinare "to bend, turn; cause to lean" (see incline (v.)). Meaning "action of bending toward" (something) is from early 15c. That of "amount of a slope" is from 1799.
inclusive (adv.): "including the stated limits in the number or sum," mid-15c., from Medieval Latin inclusivus, from Latin inclus-, past participle stem of includere "to shut in, enclose" (see include).
incoherent (adj.): 1620s, "without coherence" (of immaterial or abstract things, especially thought or language), from in- (1) "not, opposite of" + coherent. As "without physical coherence" from 1690s. Related: Incoherently.
inconvenience (n.): c. 1400, "harm, damage; danger; misfortune, affliction," from Old French inconvenience "misfortune, calamity; impropriety" (Modern French inconvenance), from Late Latin inconvenientia "lack of consistency, incongruity" (in Medieval Latin "misfortune, affliction"), noun of quality from inconvenientem (see inconvenient). Sense of "impropriety, unfitness; an improper act or utterance" in English is from early 15c. Meaning "quality of being inconvenient" is from 1650s.
incredulity (n.): "disbelieving frame of mind," early 15c., from Middle French incrédulité, from Latin incredulitatem (nominative incredulitas) "unbelief," noun of quality from incredulus "unbelieving" (see incredulous).
incredulous (adj.): "unbelieving," 1570s, from Latin incredulus "unbelieving, incredulous," from in- "not" (see in- (1)) + credulus (see credulous). Formerly also of religious beliefs. Related: Incredulously; incredulousness.
indecisive (adj.): 1726, "inconclusive," from in- (1) "not, opposite of" + decisive. Meaning "vacillating, characterized by indecision" is from 1775. Related: Indecisively; indecisiveness.
indefinitely (adv.): early 15c., "without settled limitation, boundless;" see indefinite + -ly (2).
indemnify (v.): "compensate for loss or expense," 1610s, from Latin indemnis "unhurt" (see indemnity) + -fy. Related: Indemnified; indemnifying. "Indemnify formerly meant to save a person from damage or loss, but now much more often means to make good after loss or the damage of property." [Century Dictionary]
indentation (n.1): "cut, notch, incision," 1728, of margins or edges, extended form of indent (n.).
indenture (n.): late 14c., endenture, indenture, "written formal contract for services (between master and apprentice, etc.), a deed with mutual covenants," from Anglo-French endenture, Old French endenteure "indentation," from endenter "to notch or dent" (see indent (v.1)).

Such contracts (especially between master craftsmen and apprentices) were written in full identical versions on a sheet of parchment, which was then cut apart in a zigzag, or "notched" line. Each party took one, and the genuineness of a document of indenture could be proved by laying it beside its counterpart.
indicate (v.): 1650s, "to point out," back-formation from indication (q.v.) or else from Latin indicatus, past participle of indicare "to point out, show, indicate." Especially "to give suggestion of, be reason for inferring" (1706). Related: Indicated; indicating.
indifference (n.): mid-15c., "quality of being neither good nor bad, neutral quality," from Latin indifferentia "want of difference, similarity," noun of quality from indifferentem (see indifferent). From late 15c. as "lack of prejudice, impartiality;" from 1650s as "state of being apathetic." Meaning "comparative mediocrity, inexcellence"" is from 1864.
indictment (n.): formerly also endictment, c. 1300, endytement "action of accusing," from Anglo-French and Old French enditement, from enditer "accuse, indict" (see indict). Meaning "formal legal document containing a charge proved before a grand jury" is from c. 1500. Latin spelling restored 17c.
indigent (adj.): c. 1400, from Old French indigent "poor, needy," from Latin indigentem "in want of, needing" (see indigence). As a noun, "poor person," from early 15c.
indignant (adj.): 1580s, from Latin indignantem (nominative indignans) "impatient, reluctant, indignant," present participle of indignari "to be displeased at, be offended, resent, deem unworthy" (see indignation). Related: Indignantly.
indicative (adj.): mid-15c., "that points out, states, or declares" (grammatical), from Old French indicatif (14c.), from Late Latin indicativus "serving to point out," from indicat-, past participle stem of Latin indicare "to point out, show" (see indication). The "mood in the conjugation of a Latin verb whose essential function is to state a fact (as opposed to a wish, supposition or command)" [Middle English Dictionary]. Related: Indicatively.
individualism (n.): "quality of being distinct or individual, individuality," 1815, from individual + -ism. As the name of a social philosophy favoring non-interference of government in lives of individuals (opposed to communism and socialism) first attested 1851 in writings of J.S. Mill.
individuality (n.): 1610s, "the aggregate of one's idiosyncrasies," from individual + -ity, or from Medieval Latin individualitas. Meaning "condition of existing as an individual" is from 1650s.
indolent (adj.): 1660s, "causing no pain, painless," from French indolent (16c.) or directly from Late Latin indolentem (see indolence). Sense of "living easily, slothful," is 1710, a sense perhaps developed in French. Related: Indolently.
independence (n.): 1630s, "fact of not depending on others or another, self-support and self-government;" see independent + -ence. Earlier in same sense was independency (1610s). U.S. Independence Day (July 4, commemorating events of 1776) is recorded under that name by 1791.

An Old English word for it was selfdom, with self + dom "law," but in form this is closer to privilege (n.). The two concepts are not always distinguishable.
induction (n.): late 14c., "advancement toward the grace of God;" also (c. 1400) "formal installation of a clergyman," from Old French induction (14c.) or directly from Latin inductionem (nominative inductio) "a leading in, introduction, admission," noun of action from past participle stem of inducere "to lead" (see induce).

As a term in logic (early 15c.) it is from Cicero's use of inductio to translate Greek epagoge "leading to" in Aristotle. Induction starts with known instances and arrives at generalizations; deduction starts from the general principle and arrives at some individual fact. As a term in physics, in reference to electrical influence, 1801; military service sense is from 1934, American English. Related: Inductional.
indulge (v.): formerly also endulge, 1630s, "to grant as a favor;" 1650s, "to treat with unearned favor" (in reference both to persons and desires), a back-formation from indulgence (q.v.), or else from Latin indulgere "be complaisant, be indulgent, yield; give oneself up to;" probably a compound verb with first element in- "in," but the second element is obscure. Related: Indulged; indulging; indulgingly.
industrial (adj.): 1774, "resulting from labor," from French industriel, from Medieval Latin industrialis, from Latin industria "diligence, activity" (see industry). There is an isolated earlier used in the same sense from 1580s, from Latin industria.

The main modern meaning "pertaining to the manufacture of commodities, connected with the application of industry to manufactures" is from 1830, from a sense in French.

Meaning "suitable for industrial use" is from 1904. As a style of dance music, attested from 1988. Industrial revolution was in use by 1840 to refer to what were then recent developments and changes in England and elsewhere.
industrialize (v.): 1852, from industrial + -ize. Probably modeled on French industrialiser (1842). Related: Industrialized; industrializing.
industrious (adj.): 1550s, "characterized by energy, effort, and attention; marked by industry," from Middle French industrieux (c. 1500) and directly from Late Latin industriosus, from Latin industria "diligence, activity" (see industry). Of persons, "given to industry, working diligently," 1590s. It retains the etymological sense of the Latin word while industrial serves in the modern senses. Related: Industriously; industriousness.
indulgent (adj.): "lenient, willing to overlook faults," often in a bad sense, "too lenient," c. 1500, from Latin indulgentem (nominative indulgens) "kind, tender, fond," present participle of indulgere "be kind, be complaisant, yield" (see indulgence). Related: Indulgently.
inebriated (adj.): "drunken," c. 1600, past participle adjective from inebriate. The earlier adjective was inebriate (late 15c.).
infatuation (n.): 1640s, noun of action from infatuate (q.v.), or else from French infatuation or directly from Late Latin infatuationem (nominative infatuatio), from past participle stem of Latin infatuare "make a fool of."
inference (n.): 1590s, "action of inferring;" 1610s, "that which is inferred;" from Medieval Latin inferentia, from Latin inferentem (nominative inferens), present participle of inferre "bring into; conclude, deduce" (see infer).
inheritance (n.): late 14c., enheritaunce "fact of receiving by hereditary succession;" early 15c. as "that which is or may be inherited," from Anglo-French and Old French enheritaunce, from Old French enheriter "make heir, appoint as heir" (see inherit). Heritance "act of inheriting" is from mid-15c.
inhibit (v.): early 15c., "to forbid, prohibit," back-formation from inhibition or else from Latin inhibitus, past participle of inhibere "to hold in, hold back, keep back." Psychological sense (1876) is from earlier, softened meaning of "restrain, check, hinder" (1530s). Related: Inhibited; inhibiting.
inflate (v.): early 15c., "cause to swell," from Latin inflatus (source also of Italian enfiare, Spanish inflar, French enfler), past participle of inflare "to blow into, inflate" (see inflation). Economics sense (of prices, currency, etc.) is from 1843. In some senses a back-formation from inflation. Related: Inflated; inflating.
inspirational (adj.): "tending to inspire," 1878; see inspiration + -al (1). Also "influenced by inspiration" (1839); "pertaining to inspiration" (1888). The adjective was used earlier in spiritualism. Earlier in the sense "tending to inspire" were inspirative (1770), inspiring (1640s).
inspire (v.): mid-14c., enspiren, "to fill (the mind, heart, etc., with grace, etc.);" also "to prompt or induce (someone to do something)," from Old French enspirer (13c.), from Latin inspirare "blow into, breathe upon," figuratively "inspire, excite, inflame," from in- "in" (see in- (2)) + spirare "to breathe" (see spirit (n.)).

The Latin word was used as a loan-translation of Greek pnein in the Bible. General sense of "influence or animate with an idea or purpose" is from late 14c. Also sometimes used in literal sense in Middle English. Related: Inspires; inspiring.
insouciant (adj.): 1828, from French insouciant "careless, thoughtless, heedless," from in- "not" (see in- (1)) + souciant "caring," present participle of soucier "to care," from Latin sollicitare "to agitate" (see solicit). Related: Insouciantly.
insolence (n.): late 14c., from Latin insolentia "unusualness, strangeness; excess, immoderation; haughtiness, arrogance," from insolentem "unusual; arrogant" (see insolent).