Online Etymology Dictionary

inbred (adj.): 1590s, "native, produced within," also "inherent by nature," from in + bred. The genetic sense is attested from 1892 (see inbreeding).
inbreeding (n.): "breeding of animals from the same parentage," c. 1842, from in + verbal noun from breed (v.). The older term for "to breed from animals of the same parentage" was to breed in and in (1765). The verb inbreed is attested from 1590s in the sense "produce within" (intransitive).
Inc.: U.S. abbreviation of Incorporated in company names (equivalent of British Ltd.), first attested 1904.
Inca (n.): 1590s, from Spanish Inga (1520s), from Quechea Inca, literally "lord, king." Technically only of the high Inca, but it was used widely among the Incas for "man of royal blood." Related: Incan.
incalculable (adj.): 1772, from in- (1) "not, opposite of" + calculable "that can be counted" (see calculate). Related: Incalculably; incalculability.
incandescence (n.): 1650s, figurative, "state of being 'inflamed,' " from French incandescence, from incandescent (see incandescent). Literal use from 1794.
incandescent (adj.): 1794, from French incandescent (18c.) or directly from Latin incandescentem (nominative incandescens), present participle of incandescere "become warm, glow, kindle," from in- "within" (see in- (2)) + candescere "begin to glow, become white," inceptive of candere "to glow, to shine" (see candle). In reference to electric light, from 1881. The verb incandesce (1838), originally in science, is perhaps a back-formation.
incantation (n.): late 14c., from Old French incantacion "spell, exorcism" (13c.), from Late Latin incantationem (nominative incantatio) "art of enchanting," noun of action from past participle stem of incantare "to bewitch, charm, cast a spell upon, chant magic over, sing spells" (see enchantment).
incapable (adj.): 1590s, from Middle French incapable (16c.) and directly from Medieval Latin incapabilis "incapable," from in- "not" (see in- (1)) + capabilis "receptive; able to grasp or hold" (see capable). Related: Incapably; incapability.
incapacitate (v.): 1650s in a legal sense; 1660s in general use, "deprive of natural power," from incapacity + -ate. Related: Incapacitated; incapacitating.
incapacitation (n.): 1741, noun of action from incapacitate.
incapacity (n.): 1610s, "lack of ability, powerlessness," from French incapacité (16c.), from Medieval Latin incapacitatem (nominative incapacitas), from Late Latin incapax (genitive incapacis) "incapable," from in- "not" (see in- (1)) + Latin capax "capable," literally "able to hold much," from capere "to take" (see capable). As a legal term (1640s), "lack of qualification," referring to inability to take, receive, or deal with in some way.
incarcerate (v.): "imprison, shut up in jail," 1550s, a back-formation from incarceration (q.v.), or else from Medieval Latin incarceratus, past participle of incarcerare "to imprison." Related: Incarcerated; incarcerating.
incarceration (n.): "fact of being imprisoned," 1530s, from Medieval Latin incarcerationem (nominative incarceratio), noun of action from past participle stem of incarcerare "to imprison," from in- "in" (see in- (2)) + carcer "prison, an enclosed space," from Proto-Italic *kar-kr(o)-, of uncertain origin.
It seems best to connect carcer with other IE words for 'circle, round object', such as [Latin] curvus, [Greek] κιρκος 'ring', [Old Norse] hringr, although not all of these have a good IE etymology. The reduplication in Latin carcer could be iconic; thus, the original meaning would have been 'enclosure'. [de Vaan]
The word appears earlier in English in an obsolete medical sense of "retention of pus" (early 15c.).
incarnadine: 1590s (adj.) "flesh-colored, carnation-colored, pale red, pink," from French incarnadin (16c.), from dialectal Italian incarnadino "flesh-color," from Late Latin incarnatio (see incarnation). The adjective now is archaic or obsolete. The word survives as a verb taken from the adjective, which properly would mean "to make flesh-colored," but means "make red" instead, the sense and the existence of the verb being entirely traceable to Lady Macbeth ("Macbeth" II ii.) in 1605. Its direct root might be the noun incarnadine "blood-red; flesh-color," though this is not attested until 1620s.
incarnate (v.): "clothe or embody in flesh," 1530s, a back-formation from incarnation, or else from Late Latin incarnatus "made flesh," past participle of incarnare "to make flesh; be made flesh." Meaning "make or form flesh" (as in healing a wound) is from 1670s. Related: Incarnated; incarnating.
incarnate (adj.): late 14c., "embodied in flesh, in human or bodily form" (of souls, spirits, etc.), from Late Latin incarnatus "made flesh," a frequent word among early Christian writers, past-participle adjective from Latin incarnare "to make flesh" (see incarnation). Of qualities or abstractions, 1530s.
incarnation (n.): c. 1300, "embodiment of God in the person of Christ," from Old French incarnacion "the Incarnation" (12c.), from Late Latin incarnationem (nominative incarnatio), "act of being made flesh" (used by Church writers especially in reference to God in Christ; source also of Spanish encarnacion, Italian incarnazione), noun of action from past participle stem of Late Latin incarnari "be made flesh," from in- "in" (see in- (2)) + caro (genitive carnis) "flesh" (see carnage). Glossed in Old English as inflæscnes, inlichomung. As "person or thing that is the embodiment" (of some quality, deity, etc.) from 1742.
incase (v.): variant of encase.
Theory of Incasement, an old theory of reproduction which assumed that when the first animal of each species was created, the germs of all other individuals of the same species which were to come from it were incased in its ova. The discovery of spermatozoa developed the theory in two opposite directions: the ovulists, or ovists, held still to the theory of incasement in the female while the animalculists, or spermists, entertained the theory of incasement in the male. [Century Dictionary]
incautious (adj.): 1650s, from in- (1) "not" + cautious (adj.). The Latin adjective was incautus. Related: Incautiously. Incaution (n.) is attested from 1715.
incendiarism (n.): 1670s; see incendiary + -ism. Originally figurative; the literal sense of "malicious burning" is attested from 1755.
incendiary (n.): c. 1400, "person who sets malicious fires," from Latin incendiarius "an incendiary," literally "causing a fire" (see incendiary (adj.)). Meaning "person who enflames political passions" is from 1630s.
incendiary (adj.): mid-15c., "capable of being used to set fires," from Latin incendiarius "causing a fire," from incendium "a burning, a fire, conflagration," from incendere "set on fire, light up with fire, brighten," figuratively, "incite, rouse, excite, enrage," from in- "into, in, on, upon" (see in- (2)) + candere "to shine, glow, be on fire" (see candle).

Figurative sense of "enflaming passions" is from 1610s in English. Meaning "relating to criminal burning" is from 1610s. Military use, of bombs, shells, etc., attested from 1871. The obsolete poetic verb incend is attested from c. 1500.
incensation (n.): "action of perfuming," 1851, noun of action from incense (v.2).
incense (n.): late 13c., "gum or other substance producing a sweet smell when burned," from Old French encens (12c.), from Late Latin incensum "burnt incense," literally "that which is burnt," noun use of neuter past participle of Latin incendere "set on fire" (see incendiary). Meaning "smoke or perfume of incense" is from late 14c.
incense (v.1): early 15c., encensen "to arouse, inspire," from Old French incenser, from Latin incensare, frequentative of incendere "set on fire," figuratively "incite, enrage, rouse" (see incendiary). From mid-15c. as "to provoke, anger." Literal sense "to heat, make (something) hot" is from c. 1500 in English but is rare.
incense (v.2): "to offer incense, perfume with incense, fumigate (something) with incense," late 13c., encensen, incensen, from incense (n.) or from Old French encenser (11c.), or directly from Medieval Latin incensare.
incensed (adj.): "full of wrath, inflamed with anger," 1590s, past-participle adjective from incense (v.1). Earlier it was used in heraldry, in reference to fire-breathing animals (1570s). Distinguished in pronunciation from incensed "perfumed witrh incense" (1610s), from incense (v.2).
incent (v.): by 1992, U.S. government-speak, a back-formation from incentive. Related: Incented; incenting. Compare incentivize.
incentive (n.): early 15c., "that which moves the mind or stirs the passion," from Late Latin incentivum, noun use of neuter of Latin adjective incentivus "setting the tune" (in Late Latin "inciting"), from past participle stem of incinere "strike up," from in- "in, into" (see in- (2)) + canere "to sing" (see chant (v.)). The sense apparently was influenced in Late Latin by association with incendere "to kindle." (Milton uses the adjective to mean "setting fire, incendiary.") Meaning "rewards meant to encourage harder work" is from 1948, short for incentive payment, etc. (see incentive (adj.)).
incentive (adj.): c. 1600, "provocative, exciting, encouraging," from Late Latin incentivus "inciting" (see incentive (n.)). In reference to a system of rewards meant to encourage harder work, first attested 1943 in jargon of the U.S. war economy.
incentivize (v.): by 1970, from incentive (adj.) + -ize. Related: Incentivized; incentivizing.
incept (v.): 1560s, "to commence, begin" (trans.), from Latin inceptus, past participle of incipere "to begin" (see inception). Related: Incepted; incepting.
inception (n.): early 15c., "a beginning, a starting," from Old French inception and directly from Latin inceptionem (nominative inceptio) "a beginning; an undertaking," noun of action from past participle stem of incipere "begin, take in hand," from in- "in, on" (see in- (2)) + cipere comb. form of capere "take, seize" (see capable).
inceptive (adj.): 1650s, "denoting the initial point or step," from Middle French inceptif (16c.), from Latin incept-, past participle stem of incipere "to begin" (see inception). Interchangeable with inchoative. As a noun, "an inceptive verb," from 1610s.
incertitude (n.): mid-15c., "variability," from Middle French incertitude (14c.), from Late Latin incertitudinem (nominative incertitudo) "uncertainty," from in- "not, opposite of" (see in- (1)) + certitudo "that which is certain" (see certitude). From c. 1600 as "doubt, hesitation." Middle English also had incertain "uncertain" and incertainty "uncertainty," both from Old French, but both have been displaced by forms in un-.
incessancy (n.): 1610s, from incessant + -cy.
incessant (adj.): mid-15c., from Old French *incessant or directly from Late Latin incessantem (nominative incessans) "unceasing," from Latin in- "not" (see in- (1)) + cessans, present participle of cessare "to cease" (see cease (v.)). Related: Incessantly (early 15c.).
incest (n.): "the crime of sexual intercourse between near kindred," c. 1200, from Old French inceste "incest; lechery, fornication," and directly from Latin incestum "unchastity, impious unchastity," also specifically "sexual intercourse between close relatives," noun use of neuter adjective incestus "unchaste, impure," from in- "not" (see in- (1)) + castus "pure" (see caste). Old English had sibleger "incest," literally "kin-lying."
incestuous (adj.): 1530s, from Late Latin incestuosus "incestuous," from Latin incestus "unchaste" (see incest). Figurative use is from 1744. Related: Incestuously; incestuousness.
inch (n.1): "linear measure, one-twelfth of a foot," late Old English ynce, Middle English unche (current spelling c. 1300), from Latin uncia "a twelfth part," from unus "one" (see one). An early Anglo-Saxon borrowing from Latin; not found in other Germanic languages. Transferred and figurative sense of "a very small amount, small quantity" is attested from mid-14c. As the unit of measure of rainfall from 1845. Sometimes misdivided in Middle English as a neynche. Every inch "in every respect" is from early 15c. For phrase give him an inch ... see ell.
inch (n.2): "small Scottish island," early 15c., from Gaelic innis (genitive innse) "island," from Celtic *inissi (source also of Old Irish inis, Welsh ynys, Breton enez).
inch (v.): 1590s, "move little by little" (intrans.), from inch (n.1). Meaning "drive or force by small degrees" (trans.) is from 1660s. Related: Inched; inching.
inchmeal (adv.): "by inches, inch by inch," 1580s, from inch (n.1) + Middle English meal "fixed time, period of time, occasion" (see meal (n.1)).
inchoate (adj.): "recently or just begun," 1530s, from Latin inchoatus, past participle of inchoare, alteration of incohare "commence, begin," probably originally "to hitch up," traditionally derived from in- "in" (see in- (2)) + a verb from cohum "strap (fastened to the oxen's yoke)," a word of obscure origin. De Vaan says that as, incohere "is a frequent verb, ... its meaning can easily have derived from 'to yoke a plough to a team of oxen' ..., in other words, 'to start work.' Thus, there might be a core of truth in the ancient connection of cohum with a yoke."
inchoative (adj.): 1630s, "indicating beginning or inception;" see inchoate + -ive. Especially in grammar, of verbs, "denoting the beginning of action, inceptive," 1660s.
inchworm (n.): also inch-worm, 1844, American English, from inch (v.) + worm (n.). Other old names for it included loaper caterpiller, measuring worm, and surveyor. All are from its mode of progress.
incidence (n.): early 15c., "incidental matter," from Middle French incidence (15c.), from Late Latin incidentia, from incidere "to happen, befall" (see incident (n.)). Meaning "act of coming into contact with or affecting" is from 1650s. In physics, of rays of light, etc., considered with reference to direction, from 1620s.
incident (n.): early 15c., "something which occurs casually in connection with something else," from Old French incident (13c.), and directly from Latin incidentem (nominative incidens), present participle of incidere "to fall in, fall, find the way; light upon, fall in with; fall upon, occur; happen, befall," from in- "on" (see in- (2)) + -cidere, comb. form of cadere "to fall" (see case (n.1)). Broader sense of "an occurrence viewed as a separate circumstance" is from mid-15c. Euphemistic meaning "event that might trigger a crisis or political unrest" first attested 1913.
incident (adj.): late 15c., "likely to happen," from Latin incidentem (nominative incidens), present participle of incidere "to happen, befall" (see incident (n.)). From 1620s as "occurring as a subordinate;" 1660s in literal sense "falling or striking upon."