Online Etymology Dictionary

insufficient (adj.): late 14c., from Old French insufficient (14c.) or directly from Late Latin insufficientem (nominative insufficiens) "not sufficient," from in- "not, opposite of" (see in- (1)) + sufficientem (see sufficient). Originally of persons, "inadequate, unable;" of things, "lacking in what is necessary or required," from late 15c. Related: Insufficiently.
insular (adj.): 1610s, "of or pertaining to an island," from Late Latin insularis "of or belonging to an island," from Latin insula "island" (see isle). Metaphoric sense "narrow, prejudiced" is from 1775, from notion of being isolated and cut off from intercourse with other nations or people (an image that naturally suggested itself in Great Britain). The earlier adjective in the literal sense was insulan (mid-15c.), from Latin insulanus.
insulate (v.): 1530s, "make into an island," from Late Latin insulatus "made like an island," from insula "island" (see isle). Sense of "place in an isolated situation, cause (someone or something) to be detached from surroundings" is from 1785. Electrical/chemical sense of "block from electricity or heat" (by interposition of a non-conductor) is from 1742. Related: Insulated; insulating.
insulin (n.): 1922 (earlier insuline, 1914), coined in English from Latin insula "island" (see isle and compare insula); so called because the hormone is secreted by the islets of Langerhans in the pancreas. Insuline was coined independently in French in 1909.
insult (v.): 1560s, "triumph over in an arrogant way" (obsolete), from Middle French insulter "to wrong; reproach; triumph arrogantly over," earlier "to leap upon" (14c.) and directly from Latin insultare "to assail, to make a sudden leap upon," which was used by the time of Cicero in sense of "to insult, scoff at, revile," frequentative of insilire "leap at or upon," from in- "on, at" (see in- (2)) + salire "to leap" (see salient (adj.)).

Sense of "verbally abuse, affront, assail with disrespect, offer an indignity to" is from 1610s. Related: Insulted; insulting.
insuperable (adj.): mid-14c., "unconquerable, incapable of being surmounted," from Old French insuperable (14c.) or directly from Latin insuperabilis "that cannot be passed over, unconquerable," from in- "not, opposite of" (see in- (1)) + superabilis "that may be overcome," from superare "to overcome," from superus "one that is above," from super "over" (see super-). Figurative use from 1650s. Related: Insuperably; insuperability.
insurance (n.): 1550s, "engagement to marry," a variant of ensurance "an assurance, pledge, guarantee," from Old French enseurance "assurance," from ensurer, from en- "make" (see en- (1)) + sur "safe, secure, undoubted" (see sure (adj.)).

Commercial sense of "security against loss or death in exchange for payment" is from 1650s. Assurance was the older word for this specific sense (late 16c.). Compare insure.
insure (v.): mid-15c., insuren, spelling variant of ensuren "to assure, give formal assurance" (late 14c.), also "make secure, make safe" (c. 1400), from Anglo-French enseurer, Old French ensurer, from en- "make" (see en- (1)) + seur, sur "safe, secure, undoubted" (see sure (adj.)).

The particular commercial senses of "make safe against loss by payment of premiums; undertake to ensure against loss, etc." are from mid-17c. (replacing assure in that meaning). Related: Insured; insuring.
insurgent (n.): "one who rises in revolt" against a government or its laws, 1745, from Latin insurgentem (nominative insurgens), present participle of insurgere "rise up, lift oneself; rise against; stand high, gather force," from in- "against," or here perhaps merely intensive, + surgere "to rise" (see surge (n.)).

An obsolete verb insurge (from French insurger) "to rise in opposition or insurrection" was common 16c. For verb forms 19c. writers sometimes turned to insurrectionize or insurrect.
insurmountable (adj.): 1690s, from in- (1) "not, opposite of" + surmountable. Related: Insurmountably. Brachet calls French insurmontable a "ghastly philological monster."
insurrection (n.): "an uprising against civil authority," early 15c., insurreccion, from Old French insurreccion or directly from Late Latin insurrectionem (nominative insurrectio) "a rising up," noun of action from past participle stem of insurgere "to rise up" (see insurgent).
intact (adj.): mid-15c., from Latin intactus "untouched, uninjured; undefiled, chaste; unsubdued," from in- "not" (see in- (1)) + tactus, past participle of tangere "to touch" (see tangent (adj.)).
intake (n.): c. 1800, "place where water is taken into a channel or pipe," from verbal phrase, from in (adv.) + take (v.). Meaning "act of taking in" (food, breath, etc.) is first attested 1808.
intangible (adj.): 1630s, "incapable of being touched," from French intangible (c. 1500) or directly from Medieval Latin intangibilis, from in- "not" (see in- (1)) + Late Latin tangibilis "that may be touched" (see tangible). Figurative sense of "that cannot be grasped by the mind" is from 1880. Noun meaning "anything intangible" is from 1909. Related: Intangibly.
integer (n.): "a whole number" (as opposed to a fraction), 1570s, from Latin integer (adj.) "intact, whole, complete," figuratively, "untainted, upright," literally "untouched," from in- "not" (see in- (1)) + root of tangere "to touch," from PIE root *tag- "to touch, handle" (see tangent (adj.)). The word was used earlier in English as an adjective in the Latin sense, "whole, entire" (c. 1500).
integral (adj.): late 15c., "of or pertaining to a whole; intrinsic, belonging as a part to a whole," from Middle French intégral (14c.), from Medieval Latin integralis "forming a whole," from Latin integer "whole" (see integer). Related: Integrally. As a noun, 1610s, from the adjective.
integrate (v.): 1630s, "to render (something) whole, bring together the parts of," from Latin integratus, past participle of integrare "make whole," from integer "whole, complete," figuratively, "untainted, upright," literally "untouched," from in- "not" (see in- (1)) + root of tangere "to touch," from PIE root *tag- "to touch, handle" (see tangent (adj.)).

The meaning "put together parts or elements and combine them into a whole" is from 1802. The "racially desegregate" sense (1940) probably is a back-formation from integration. Related: Integrated; integrating.
integrity (n.): c. 1400, "innocence, blamelessness; chastity, purity," from Old French integrité or directly from Latin integritatem (nominative integritas) "soundness, wholeness, completeness," figuratively "purity, correctness, blamelessness," from integer "whole" (see integer). Sense of "wholeness, perfect condition" is mid-15c.
integument (n.): 1610s, from Latin integumentum "a covering," from integere "to cover over," from in- "in, upon" (see in- (2)) + tegere "to cover" (see stegosaurus). Specific sense in biology is from 1660s.
intellect (n.): "the sum of the cognitive facilities (except sense or sense and imagination), the capacity for reasoning truth," late 14c. (but little used before 16c.), from Old French intellect "intellectual capacity" (13c.), and directly from Latin intellectus "discernment, a perception, understanding," noun use of past participle of intelligere "to understand, discern" (see intelligence). The Latin word was used to translate Greek nous "mind, thought, intellect" in Aristotle.
intelligence (n.): late 14c., "the highest faculty of the mind, capacity for comprehending general truths;" c. 1400, "faculty of understanding, comprehension," from Old French intelligence (12c.) and directly from Latin intelligentia, intellegentia "understanding, knowledge, power of discerning; art, skill, taste," from intelligentem (nominative intelligens) "discerning, appreciative," present participle of intelligere "to understand, comprehend, come to know," from inter- "between" (see inter-) + legere "choose, pick out, read" (see lecture (n.)).

Meaning "superior understanding, sagacity, quality of being intelligent" is from early 15c. Sense of "information received or imparted, news" first recorded mid-15c., especially "secret information from spies" (1580s). Meaning "a being endowed with understanding or intelligence" is late 14c. Intelligence quotient first recorded 1921 (see I.Q.).
intelligible (adj.): late 14c., "able to understand, intelligent," from Latin intelligibilis, intellegibilis "that can understand; that can be understood," from intellegere "to understand, come to know" (see intelligence). In Middle English also "to be grasped by the intellect" (rather than the senses). In English, sense of "capable of being understood, that can be understood" first recorded c. 1600. Related: Intelligibly.
intemperate (adj.): "characterized by excessive indulgence in a passion or appetite," late 14c., from Latin intemperatus "excessive, immoderate," from in- "not, opposite of" (see in- (1)) + temperatus "restrained, regulated, limited, moderate, sober, calm, steady," past participle of temperare "to moderate" (see temper (v.)). Related: Intemperately.
intend (v.): c. 1300, entenden, "direct one's attention to, pay attention, give heed," from Old French entendre, intendre "to direct one's attention" (in Modern French principally "to hear"), from Latin intendere "turn one's attention, strain (in quest of something), be zealous," literally "stretch out, extend," from in- "toward" (see in- (2)) + tendere "to stretch" (see tenet).

Sense of "have as a plan, have in mind or purpose" (late 14c.) was present in Latin. A Germanic word for this was ettle, from Old Norse ætla "to think, conjecture, propose," from Proto-Germanic *ahta "consideration, attention" (source also of Old English eaht, German acht). Related: Intended; intending.
-ing (1): suffix attached to verbs to mean their action, result, product, material, etc., from Old English -ing, also -ung, from Proto-Germanic *-unga-, *-inga- (cognates: Old Norse -ing, Dutch -ing, German -ung). In early use often denoting completed or habitual action; its use has been greatly expanded in Middle and Modern English.
ingenious (adj.): early 15c., "intellectual, talented," from Middle French ingénieux "clever, ingenious" (Old French engeignos), from Latin ingeniosus "of good natural capacity, full of intellect, clever, gifted with genius," from ingenium "innate qualities, ability; inborn character," literally "that which is inborn," from in- "in" (see in- (2)) + gignere, from PIE *gen(e)-yo-, suffixed form of root *gen- "to give birth, beget, produce" (see genus).

Sense of "skillful, crafty, clever at contrivance" first recorded 1540s; earlier in this sense was Middle English enginous (mid-14c.), from Old French engeignos. Middle English also had engineful "skillful (in war)" (c. 1300). By a direct path, Latin ingenium produced Middle English ingeny "intellectual capacity, cleverness" (early 15c.), but this is obsolete. Compare engine. Related: Ingeniously; ingeniousness.
ingenue (n.): "young woman who displays innocent candor or simplicity," 1848, from French ingénue "artless girl," especially as a character on the stage, noun use of fem. of ingénu "ingenuous, artless, simple" (13c.), from Latin ingenuus "frank, upright, candid," originally "free-born" (see ingenuous). Italicized in English into 20c.
ingenuity (n.): 1590s, "honor, nobility," from Middle French ingénuité "quality of freedom by birth" and directly from Latin ingenuitatem (nominative ingenuitas) "condition of a free-born man," figuratively "frankness, generosity, noble-mindedness," from ingenuus "frank, candid, noble" (see ingenuous).

Etymologically, this word belongs to ingenuous, but in 17c. ingenious "intellectual, talented" and ingenuous so often were confused (even by Shakespeare) that ingenuity in English has come to mean only "capacity for invention or construction." That sense of this word is first attested 1640s; the word for it in Middle English was ingeniosity (the native word is craftiness). French ingénuité has evolved through "natural and graceful freedom of manners" to "graceful simplicity" (compare ingenue); for the sense "ingeniousness," French uses ingénuosité.
ingenuous (adj.): 1590s, "noble in nature, high-minded; honorably straightforward," from Latin ingenuus "with the virtues of freeborn people, of noble character, frank, upright, candid," originally "native, freeborn," literally "born in (a place)," from in- "in" (see in- (2)) + PIE *gen(e)-wo-, suffixed form of root gene- "to give birth, beget, produce" (see genus). Sense of "artless, innocent" is 1670s, via evolution from "honorably open, straightforward," to "innocently frank." Related: Ingenuously; ingenuousness.
ingest (v.): 1610s, "to take in as food," from Latin ingestus, past participle of ingerere "to throw in, pour in, heap upon," from in- "into" (see in- (2)) + gerere "to carry" (see gest). Related: Ingested; ingesting.
ingle (n.1): "fireplace," c. 1500, from Scottish, usually said to be from Gaelic aingeal "fire, light" ("but there are difficulties" [OED]), a word of uncertain origin. The vogue for Scottish poetry in late 18c. introduced ingleside "fireside" (1747) and ingle-nook "corner by the fire" (1773) to literary English.
inglorious (adj.): "with bad fame, dishonorable," 1570s, from in- (1) "not, opposite of" + glorious. Latin ingloriosus meant "without fame, unhonored, inconspicuous, without trophies." The classical sense "without fame, obscure" is attested in the English word from 1590s but is marked "rare" in OED. Related: Ingloriously; ingloriousness.
ingot (n.): late 14c., "mold in which metal is cast," probably from in- (2) "in" + Old English goten, past participle of geotan "to pour" (see found (v.2)). Sense of "mass of cast metal" first attested early 15c.
ingrain (v.): see engrain, or ingrained.
ingrate (n.): "ungrateful person," 1670s, from earlier adjective meaning "unfriendly," also "ungrateful, unthankful" (14c.), from Latin ingratus "unpleasant, disagreeable," also "ungrateful, unthankful," and "thankless, unprofitable," from in- "not" (see in- (1)) + gratus "pleasing, beloved, dear, agreeable" (see grace (n.)).
ingratiate (v.): 1620s, possibly via 16c. Italian ingraziarsi "to bring (oneself) into favor," or an unrecorded Medieval Latin *ingratiatus, from Latin phrase in gratiam "for the favor of," from in "in" (see in- (2)) + gratia "favor, grace" (see grace (n.)). Related: Ingratiated; ingratiating.
ingratitude (n.): mid-14c., from Old French ingratitude "ungratefulness" (13c.) and directly from Late Latin ingratitudinem (nominative ingratitudo) "unthankfulness," noun of quality from Latin ingratus "ungrateful" (see ingrate).
ingredient (n.): in early use also engredient, early 15c., "something forming part of a mixture," from Latin ingredientem (nominative ingrediens) "that which enters into" (a compound, recipe, etc.), present participle of ingredi "go in, enter," from in- "in" (see in- (2)) + gradi "to step, go" (see grade (n.)). Also from early 15c. as an adjective, "forming part of a mixture."
ingress (n.): mid-15c., from Latin ingressus "an advance; walking; an entry," from ingress-, past participle stem of ingredi "to step into, enter," from in- "in" (see in- (2)) + gradi "to step, go" (see grade (n.)). The verb meaning "to enter, go in" sometimes said to be American English, but it is attested from early 14c.
ingrown (adj.): also in-grown, 1660s, "native, innate," from in + grown. Of nails, "that has grown into the flesh," 1869 (in-growing in this sense is from 1847). Related: Ingrowth (1870).
inguinal (adj.): 1680s, from French inguinal (16c.) or directly from Latin inguinalis "of the groin," from inguen (genitive inguinis) "groin," from PIE *engw- "groin, internal organ" (source also of Greek aden "gland"). Related: Inguinally.
inhabit (v.): late 14c., from Old French enhabiter, enabiter "dwell in, live in, reside" (12c.), from Latin inhabitare "to dwell in," from in- "in" (see in- (2)) + habitare "to dwell," frequentative of habere "hold, have" (see habit (n.)). Formerly also enhabit. Related: Inhabited; inhabiting.
inhale (v.): 1725, "to breathe in, draw air into the lungs," a back-formation from inhalation or else from French inhaler in this sense; used as a word to be the opposite of exhale. Slang sense of "eat rapidly" is recorded from 1924. As a noun, "act of inhaling," by 1904. Related: Inhaled; inhaling.
inherent (adj.): 1570s, from Latin inhaerentem (nominative inhaerens), present participle of inhaerere "be closely connected with, be inherent," literally "adhere to, cling to," from in- "in" (see in- (2)) + haerere "to stick" (see hesitation). Related: Inherently.
inherit (v.): c. 1300, "to make (someone) an heir" (a sense now obsolete), from Old French enheriter "make heir, attribute the right of inheretance to, appoint as heir," from Late Latin inhereditare "to appoint as heir," from in- "in" (see in- (2)) + Latin hereditare "to inherit," from heres (genitive heredis) "heir" (see heredity).

Sense of "receive inheritance, get by succession as representative of the former possessor" is attested from mid-14c.; in Medieval Latin inhereditare also had taken on a sense "put in possession." Original sense is retained in disinherit. Related: Inherited; inheriting; inheritable.
inhibition (n.): late 14c., "formal prohibition; interdiction of legal proceedings by authority;" also, the document setting forth such a prohibition, from Old French inibicion and directly from Latin inhibitionem (nominative inhibitio) "a restraining," from past participle stem of inhibere "to hold in, hold back, keep back," from in- "in, on" (see in- (2)) + habere "to hold" (see habit (n.)). Psychological sense of "involuntary check on an expression of an impulse" is from 1876.
inhospitable (adj.): 1560s, from Middle French inhospitable (15c.), from Medieval Latin inhospitabilis (equivalent of Latin inhospitalis), from in- "not" (see in- (1)) + Medieval Latin hospitabilis (see hospitable).
inhuman (adj.): mid-15c., "cruel," from Latin inhumanus "inhuman, savage, cruel, rude, barbarous," from in- "not, opposite of" (see in- (1)) + humanus "human" (see human). Spelled inhumane till 18c. (see humane).
inhumane (adj.): originally a variant spelling and pronunciation of inhuman "cruel, hard-hearted;" it appears to have died out 17c. but returned c. 1822, probably a reformation as a negative of humane (q.v.), with its accent.
inhume (v.): "bury, lay in the grave," c. 1600, from Latin inhumare "to bury," literally "to put into the ground," from in- "in" (see in- (2)) + humus "earth, soil" (see humus). Related: Inhumed; inhuming.