Online Etymology Dictionary

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.
integrated (adj.): 1580s, "combined into a whole," past participle adjective from integrate (v.). Sense of "desegregated, not or no longer divided by race, etc." is from 1947.
integration (n.): 1610s, "act of bringing together the parts of a whole," from French intégration and directly from Late Latin integrationem (nominative integratio) "renewal, restoration," noun of action from past participle stem of Latin integrare "make whole," also "renew, begin again" (see integrate). Anti-discrimination sense (opposed to segregation) is recorded from 1934.
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.
integumentary (adj.): 1826, from integument + -ary.
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.
intellection (n.): c. 1400, intellecioun "meaning, purpose;" mid-15c., "the understanding;" 1610s, "an act of understanding," from Old French intelleccion and directly from Medieval Latin intellectionem (nominative intellectio), noun of action from past participle stem of Latin intelligere "to understand, discern" (see intelligence).
intellectual (adj.): late 14c., "grasped by the understanding" (rather than by the senses), from Old French intellectuel (13c.) and directly from Latin intellectualis "relating to the understanding," from intellectus "discernment, understanding," noun use of past participle of intelligere "to understand, discern" (see intelligence).

Sense of "characterized by a high degree of intellect" is from 1819. Meaning "appealing to or engaging the mental powers" is from 1834. Intellectual property "products of the intellect" is attested from 1845. Adjective formations in the sense "of or pertaining to the intellect" included intellective (early 15c.), intellectile (1670s).
intellectual (n.): 1590s, "mind, intellect, intellectual powers," from intellectual (adj.). The meaning "an intellectual person" is attested from 1650s but was hardly used in that sense in 19c. and the modern use in this sense seems to be a re-coinage from c. 1906. Related: Intellectuals.
intellectualism (n.): 1818, in philosophy, "belief in the supremacy of the intellect," probably based on German Intellektualismus (said by Klein to have been coined 1803 by Friedrich Wilhelm Joseph von Schelling (1775-1854) from Late Latin intellectualis); see intellectual + -ism. Meaning "devotion to intellectuality" also is from 1818.
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).
intellectualization (n.): 1821, noun of action from intellectualize.
intellectualize (v.): 1819 (Coleridge), "infuse with intellectual quality," from intellectual + -ize. From 1827 as "exercise the mind, reason upon a matter of intellect." Related: Intellectualized; intellectualizing.
intellectually (adv.): late 14c., "to or by the understanding," from intellectual + -ly (2).
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.).
intelligencer (n.): 1580s, "spy, informant," agent noun from intelligence. Perhaps modeled on French intelligencier or Italian intelligentiere. Meaning "bringer of news, one who conveys intelligence" is from 1630s; as a newspaper name from 1640s.
intelligent (adj.): c. 1500, a back-formation from intelligence or else from Latin intelligentem (nominative intelligens), present participle of intelligere. Intelligent design, as a name for an alternative to atheistic cosmology and the theory of evolution, is from 1999. Related: Intelligently.
intelligentsia (n.): "the intellectual class collectively," 1905, from Russian intelligyentsiya, from Latin intelligentia "intelligence" (see intelligence). Perhaps via Italian intelligenzia.
intelligibility (n.): 1670s, from intelligible + -ity.
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.
intemperance (n.): early 15c., "lack of restraint, excess," also of weather, "inclemency, severity," from Old French intemperance (14c.) and directly from Latin intemperantia "intemperateness, immoderation, excess" (as in intemperantia vini "immoderate use of wine"), from in- "not, opposite of" (see in- (1)) + temperantia "moderation, sobriety, discretion, self-control," from temperans, present participle of temperare "to moderate" (see temper (v.)).
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.
intendant (n.): "one who has charge of some business," 1650s, from French intendant (16c.), from Latin intendantem, present participle of intendere "turn one's attention, exert oneself" (see intend).
intended (n.): "one's intended husband or wife," 1767, noun use of past participle of intend (v.).
intense (adj.): early 15c., of situations or qualities, "great, extreme," from Old French intense (13c.), from Latin intensus "stretched, strained, high-strung, tight," originally past participle of intendere in its literal sense of "stretch out, strain" (see intend). From 1630s of persons, "high-strung." Related: Intensely; intenseness.
intensification (n.): 1835, noun of action from intensify.
intensify (v.): 1817 (transitive), from intense + -ify, first attested in Coleridge, in place of intend, which he said no longer was felt as connected with intense. Intransitive sense is from 1845. Middle English used intensen (v.) "to increase (something), strengthen, intensify," early 15c. Related: Intensified; intensifying.
I am aware that this word [intensifying] occurs neither in Johnson's Dictionary nor in any classical writer. But the word, "to intend," which Newton and others before him employ in this sense, is now so completely appropriated to another meaning, that I could not use it without ambiguity: while to paraphrase the sense, as by render intense, would often break up the sentence and destroy that harmony of the position of the words with the logical position of the thoughts, which is a beauty in all composition, and more especially desirable in a close philosophical investigation. I have therefore hazarded the word, intensify; though, I confess, it sounds uncouth to my own ear. [Coleridge, footnote in "Biographia Literaria," 1817]
intension (n.): c. 1600, "action of stretching; increase of degree or force," from Latin intensionem/intentionem (nominative intensio/intentio) "a stretching, straining," figuratively "exertion, effort," noun of action from past participle stem of intendere in its literal sense of "stretch out, strain" (see intend, and compare intention, which has the figurative sense). Related: Intensional.
intensity (n.): 1660s, from intense + -ity. Earlier was intenseness (1610s). A scientific term originally; sense of "extreme depth of feeling" attested by 1830.
intensive (adj.): mid-15c., "intense, fervent, great," from Old French intensif (14c.) and Medieval Latin intensivus, from Latin intens-, past participle stem of intendere "turn one's attention; strain, stretch" (see intend).

Grammatical meaning "expressing intensity" is from c. 1600; as a noun, "something expressing intensity," 1813, from the adjective. Alternative intensitive is a malformation. Intensive care attested from 1958. Related: Intensively; intensiveness.
intent (n.): "purpose," early 13c., from Old French entent, entente "goal, end, aim, purpose; attention, application," and directly from Latin intentus "a stretching out," in Late Latin "intention, purpose," noun use of past participle of intendere "stretch out, lean toward, strain," literally "to stretch out" (see intend). In law, "state of mind with respect to intelligent volition" (17c.).
intent (adj.): late 14c., "very attentive, eager," from Latin intentus "attentive, eager, waiting, strained," past participle of intendere "to strain, stretch" (see intend). Sense of "having the mind fixed (upon something)" is from c. 1600. Related: Intently.
intention (n.): late 14c., entencioun, "purpose, design, aim or object; will, wish, desire, that which is intended," from Old French entencion "intent, purpose, aspiration; will; thought" (12c.), from Latin intentionem (nominative intentio) "a stretching out, straining, exertion, effort; attention," noun of action from intendere "to turn one's attention," literally "to stretch out" (see intend). Also in Middle English "emotion, feelings; heart, mind, mental faculties, understanding."
intentional (adj.): 1520s, from intention + -al (1) or else from Medieval Latin intentionalis. Intentional fallacy recorded from 1946. Related: Intentionality.
intentionally (adv.): "on purpose," 1660s; see intentional + -ly (2). Middle English had the phrase of entencioun (1420) "on purpose, intentionally."
intentioned (adj.): "having intentions" (of a specified kind), 16c., from intention + -ed.
intentions (n.): "one's purposes with regard to courtship and marriage," by 1796; see intention.
intentive (adj.): late 14c., "eager, assiduous; attentive, paying attention," from Old French ententif, intentif "attentive, solicitous, assiduous" (12c.), from Late Latin intentivus, from intent-, past participle stem of Latin intendere "turn one's attention" (see intend). Related: Intentively; intentiveness.
inter (v.): "bury in the earth or a grave," c. 1300, formerly also enter, from Old French enterer (11c.), from Medieval Latin interrare "put in the earth, bury," from in- "in" (see in- (2)) + Latin terra "earth" (see terrain). Related: Interred; interring.
inter alia: Latin, literally "amongst other things." from inter "among, between" (see inter-) + alia, neuter accusative plural of alius "(an)other" (see alias (adv.)). Latin for "among other persons" is inter alios.
inter-: word-forming element used freely in English, "between, among, during," from Latin inter (prep., adv.) "among, between, betwixt, in the midst of" (also used extensively as a prefix), from PIE *enter "between, among" (source also of Sanskrit antar, Old Persian antar "among, between," Greek entera (plural) "intestines," Old Irish eter, Old Welsh ithr "among, between," Gothic undar, Old English under "under"), a comparative of *en "in" (see in (adv.)).

A living prefix in English from 15c. and used with Germanic as well as Latinate words. Spelled entre- in French; most words borrowed into English in that form were re-spelled 16c. to conform with Latin except entertain, enterprise. In Latin, spelling shifted to intel- before -l-, hence intelligence, etc.
inter-war (adj.): 1939, in reference to the period between the world wars, from inter- + war (n.).
interact (v.): "act on each other, act reciprocally," 1805, from inter- + act (v.). Related: Interacted; interacting.
interaction (n.): 1812, from inter- + action.
interactive (adj.): "acting upon or influencing each other," 1832, from interact (v.), probably on model of active. Related: Interactively; interactivity.