Online Etymology Dictionary

insolvent (adj.): 1590s, "unable to pay one's debts," from in- (1) "not" + Latin solventem "paying" (see solvent). Originally of one who was not a trader; only traders could become bankrupt.
insomnia (n.): "chronic inability to sleep," 1620s, insomnie, from Latin insomnia "want of sleep, sleeplessness," from insomnis "sleepless," from in- "not" (see in- (1)) + somnus "sleep" (see Somnus). The re-Latinized form is from 1758.
insomniac: 1877 (adj.); 1879 (n.), from insomnia. Earlier was insomnious (1650s).
insomuch (adv.): late 14c. as a phrase; tending to be run together from 16c.; see in (adv.) + so + much, and compare inasmuch.
insouciance (n.): 1820, from French insouciance "heedless indifference or unconcern," from insouciant "carelessness, thoughtlessness, heedlessness," from in- "not" (see in- (1)) + souciant "caring," present participle of soucier "to care," from Latin sollicitare "to agitate" (see solicit).
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.
inspect (v.): 1620s, from Latin inspectus, past participle of inspicere "look at, observe, view; look into, inspect, examine," from in- "into" (see in- (2)) + specere "to look" (see scope (n.1)). Related: Inspected; inspecting.
inspection (n.): late 14c., from Old French inspeccion "inspection, examination" (13c., Modern French inspection), from Latin inspectionem (nominative inspectio) "a looking into," noun of action from past participle stem of inspicere "look at, observe, view; look into, inspect, examine," from in- "into" (see in- (2)) + specere "to look" (see scope (n.1)). Related: Inspectional.
inspector (n.): c. 1600, "overseer, superintendent," from Latin inspector "one who views or observes," agent noun from past participle stem of inspicere "look at, observe, view; look into, inspect, examine," from in- "into" (see in- (2)) + specere "to look" (see scope (n.1)). As a police ranking between sergeant and superintendent, it dates from 1840. Related: Inspectorial (1752). Of the 18c. feminine formations, inspectrix (1703) is earlier than inspectress (1737).
inspectorate (n.): 1762, "function or office of an inspector," from inspector + -ate (1). From 1853 as "district under the supervision of an inspector."
inspiration (n.): c. 1300, "immediate influence of God or a god," especially that under which the holy books were written, from Old French inspiracion "inhaling, breathing in; inspiration" (13c.), from Late Latin inspirationem (nominative inspiratio), noun of action from past participle stem of Latin inspirare "blow into, breathe upon," figuratively "inspire, excite, inflame," from in- "in" (see in- (2)) + spirare "to breathe" (see spirit (n.)).
And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. [Gen. ii.7]
The sense evolution seems to be from "breathe into" to "infuse animation or influence," thus "affect, rouse, guide or control," especially by divine influence. Inspire (v.) in Middle English also was used to mean "breath or put life or spirit into the human body; impart reason to a human soul." Literal sense "act of inhaling" attested in English from 1560s. Meaning "one who inspires others" is attested by 1867.
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.
inspired (adj.): c. 1400, "communicated by divine or supernatural powers," past-participle adjective from inspire (v.). From 1660s as "infused with seemingly supernatural influence."
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.
inspissate (v.): "make thick or thicker," 1620s, from Late Latin inspissatus, past participle of inspissare, from in- "in, into" (see in- (2)) + Latin spissare "to thicken," related to spissus "thick" (see spissitude). Related: Inspissated; inspissating.
inspissation (n.): c. 1600, from Medieval Latin inspissationem (nominative inspissatio), noun of action from past participle stem of inspissare, from in- "in, into" (see in- (2)) + Latin spissare "to thicken," related to spissus "thick" (see spissitude).
instability (n.): early 15c., from Old French instabilité "inconstancy" (15c.) or directly from Latin instabilitatem (nominative instabilitas) "unsteadiness," from instabilis "unsteady, not firm, inconstant, fickle," from in- "not, opposite of" (see in- (1)) + stabilis (see stable (adj.)).
instable (adj.): c. 1400, from Latin instabilis "unsteady, not firm, inconstant, fickle," from in- "not, opposite of" (see in- (1)) + stabilis (see stable (adj.)). Now mostly replaced by unstable.
install (v.): also instal, formerly also enstall, early 15c., "place in (ecclesiastical) office by seating in an official stall," from Old French installer (14c.) or directly from Medieval Latin installare, from Latin in- "in" (see in- (2)) + Medieval Latin stallum "stall," from a Germanic source (compare Old High German stal "standing place;" see stall (n.1)). Related: Installed; installing.
In the church of England the installation of a canon or prebendary of a cathedral consists in solemnly inducting him into his stall in the choir and his place in the chapter. [Century Dictionary]
installation (n.): mid-15c., "action of installing," in reference to church offices or other positions, from Medieval Latin installationem (nominative installatio), noun of action from past participle stem of installare (see install). Of machinery, etc., "act of setting up, a placing in position for use," from 1882.
installment (n.): also instalment, 1580s, "induction into office, act of installing," from install + -ment.

The word meaning "a partial payment on account of debt due" (1776) earlier referred to the arrangement of payment (1732), and is an alteration of Anglo-French estaler "to fix payments," from Old French estal "fixed position, place; stall of a stable, market, or choir," from a Germanic source akin to Old High German stal "standing place" (see stall (n.1)). General sense of "a part of a whole, furnished or produced in advance of the rest" is from 1823. Installment plan is from 1894.
Instamatic: 1962, proprietary name (reg. Eastman Kodak Co., Rochester, N.Y.) for a type of self-loading camera, from instant + automatic.
instance (n.): late 14c., "urgency, insistence" (a sense now archaic), from Old French instance "effort, application; urgency, eagerness, anxiety" (13c.), from Latin instantia "presence, effort, intention; earnestness, urgency," literally "a standing near," from instans (see instant).

In logic, "a fact, a case, an example" (a sense in English from early 15c.), from Medieval Latin instantia, which translated Greek enstasis. This led to for instance "as an example" (1650s), and the noun phrase give (someone) a for instance (1953, American English). The general sense "anything that illustrates a general type" was in use by 19c.
instance (v.): "cite as an instance" (in the logical sense), c. 1600, from instance (n.). Middle English had a verb instauncen "to plead with, urge, entreat." Related: Instanced; instancing.
instant (n.): late 14c., "moment in time, infinitely short space of time," from noun use of Old French instant "near, immediate, at hand; assiduous, urgent" (see instant (adj.)). Related: Instanted; instanting.
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).
instantaneous (adj.): 1650s, from instant (n.) on model of spontaneous, etc. Related: Instantaneously (1640s); instantaneousness; instantaneity.
instanter (adv.): "instantly," 1680s, from Latin instanter "urgently, pressingly," in Medieval Latin, "presently, at once," from Latin instans "present, pressing, urgent," literally "standing near" (see instant (adj.)).
instantiate (v.): "represent by an instance," 1946, from instance (Latin instantia) + -ate. Related: Instantiated; instantiation.
instantly (adv.): late 15c., "urgently, persistently," from instant (adj.) + -ly (2). Meaning "immediately, without any intervening time" is 1550s.
instate (v.): also enstate, "to put someone in a certain state or condition," c. 1600, from in + state (n.1). Related: Instated; instating.
instatement (n.): "act of instating," 1670s, from instate + -ment.
instauration (n.): "restoration, renewal," c. 1600, from Latin instaurationem (nominative instauratio) "a renewal," noun of action from last participle stem of instaurare, from in- "in" (see in- (2)) + -staurare (ending also found in restaurant), from PIE *stau-ro-, from root *stā- "to stand, set down, make or be firm," with derivatives meaning "place or thing that is standing" (see stet).
instead (adv.): 1590s, contraction of Middle English prepositional phrase ine stede (early 13c.; see stead), itself a loan-translation of Latin in loco (French en lieu de). Typically written as two words until mid-17c.
instellation (n.): "a putting among the stars," 1795, from in- (2) "in" + noun of action from Latin stellare "to set with stars," from stella (see star (n.)). Perhaps modeled on earlier French instellation.
instep (n.): "arch of the foot," mid-15c., apparently from in + step, "though this hardly makes sense" [Weekley]. An Old English word for "instep" was fotwelm. Middle English also had a verb instep "to track, trace" (c. 1400). Old English instæpe (n.) meant "an entrance."
instigate (v.): 1540s, back-formation from instigation or else from Latin instigatus, past participle of instigare "to urge on, incite" (source also of French instiguer). Related: Instigated; instigates; instigating.
instigation (n.): early 15c., "urging, incitement; impelling force," from Middle French instigation "instigation," and directly from Latin instigationem (nominative instigatio), noun of action from past participle stem of instigare "urge on, incite," from in- "in" (see in- (2)) + *stigare, a root meaning "to prick," from PIE root *steig- "to prick, stick, pierce" (see stick (v.)).
instigator (n.): 1590s, from Latin instigator "a stimulator," agent noun from instigare "urge on, incite" (see instigation). The classical Latin fem. form instigatrix is recorded in English from 1610s.
instill (v.): also instil, early 15c., "to introduce (liquid, feelings, etc.) little by little," from Latin instillare "put in by drops; to drop, trickle," from in- "in" (see in- (2)) + stilla "a drop" (see distill). Related: Instilled; instiller; instilling.
instillation (n.): 1540s, from Latin instillationem (nominative instillatio) "a dropping in," noun of action from past participle stem of instillare "put in by drops; to drop, trickle," from in- "in" (see in- (2)) + stilla "a drop" (see distill).
instinct (n.): early 15c., "a prompting" (a sense now obsolete), from Old French instinct (14c.) or directly from Latin instinctus "instigation, impulse, inspiration," noun use of past participle of instinguere "to incite, impel," from in- "into, in, on, upon" (see in- (2)) + stinguere "prick, goad," from PIE *steig- "to prick, stick, pierce" (see stick (v.)).

Meaning "animal faculty of intuitive perception" is from mid-15c., from notion of "natural prompting." General sense of "natural tendency" is first recorded 1560s.
Instinct is said to be blind--that is, either the end is not consciously recognized by the animal, or the connection of the means with the end is not understood. Instinct is also, in general, somewhat deficient in instant adaptability to extraordinary circumstances. [Century Dictionary]
instinctive (adj.): 1640s, from Latin instinct-, past participle stem of instinguere "to incite, impel" (see instinct) + -ive. Related: Instinctively (1610s); instinctiveness. Coleridge uses instinctivity.
instinctual (adj.): 1841, from instinct (Latin instinctus) + -al (1). Related: Instinctually.
institute (v.): early 14c., "to establish in office, appoint," from Latin institutus, past participle of instituere "to set up, put in place; arrange; found, establish; appoint, designate; govern, administer; teach, instruct," from in- "in" (see in- (2)) + statuere "establish, to cause to stand," from PIE root *stā- "to stand," with derivatives meaning "place or thing that is standing" (see stet). General sense of "set up, found, introduce" first attested late 15c. Related: Instituted; instituting.
institute (n.): 1510s, "purpose, design," from Latin institutum "an ordinance; a purpose; a custom; precedents; principal components," literally "thing set up," noun use of neuter past participle of instituere "to set up, put in place; arrange; found, establish" (see institute (v.)).

From 1540s in English as "an established law." The sense of "an organization or society devoted to some specific work," especially literary or scientific, is from 1828, from French use in Institut national des Sciences et des Arts (established 1795); Dutch instituut, German Institut also are from French. The specialized (mostly U.S.) sense "travelling academy for teachers in a district" is from 1839.
A "Teachers' Institute" is a meeting composed of teachers of Common Schools, assembled for the purpose of improvement in the studies they are to teach, and in the principles by which they are to govern. It is the design of a Teachers' Institute to bring together those who are actually engaged in teaching Common Schools, or who propose to become so, in order that they may be formed into classes and that these classes, under able instructers, may be exercised, questioned and drilled, in the same manner that the classes of a good Common School are exercised, questioned and drilled. [Horace Mann, secretary's report to the Boston Board of Education, Sept. 1, 1845]
institution (n.): c. 1400, "action of establishing or founding (a system of government, a religious order, etc.)," from Old French institucion "foundation; thing established" (12c.), from Latin institutionem (nominative institutio) "a disposition, arrangement; instruction, education," noun of state from institutus (see institute (v.)).

Meaning "established law or practice" is from 1550s. Meaning "establishment or organization for the promotion of some charity" is from 1707. Jocular or colloquial use for "anything that's been around a long time" is from 1837.
institutional (adj.): 1610s, "of or pertaining to an institution," from institution + -al (1). Related: Institutionally.
institutionalization (n.): 1898, noun of action from institutionalize (q.v.).