Online Etymology Dictionary

incidental (adj.): "casual, occurring casually in connection with something else; of minor importance," 1640s, from Medieval Latin incidentalis, from incidens (see incident (n.)). The earlier adjective in this sense was incident (1520s). Incidentals (n.) "'occasional' expenses, etc.," is attested by 1707. Incidental music "background music," originally in operas, is from 1812.
incidentally (adv.): 1520s, "by the way, casually;" see incidental + -ly (2). Sense of "as a new but related point" attested by 1925.
incinerate (v.): "burn to ashes" (transitive), 1550s, from Medieval Latin incineratus, past participle of incinerare "reduce to ashes," from in- "into" (see in- (2)) + a verb from Latin cinis (genitive cineris) "ashes," from PIE root *keni- "dust, ashes" (source also of Greek konis "dust"). Middle English had the word, from Latin, but only as a past-participle adjective meaning "reduced to ashes" (early 15c.). Related: Incinerated; incinerating.
incineration (n.): "act of burning to ashes," 1520s, from Middle French incinération (14c.), from Medieval Latin incinerationem (nominative incineratio), noun of action from past participle stem of incinerare "reduce to ashes" (see incinerate).
incinerator (n.): "device for waste disposal by burning," 1872, from incinerate + Latinate agent noun suffix -or.
incipience (n.): "beginning, commencement," 1792, from incipient + -ence. Incipiency is from 1764.
incipient (adj.): "beginning, commencing," 1660s, from Latin incipientem (nominative incipiens), present participle of incipere "begin, take up; have a beginning, originate," from in- "into, in, on, upon" (see in- (2)) + -cipere, comb. form of capere "to take" (see capable). Related: Incipiently.
incipit: opening word of a Latin book or manuscript, Latin, literally "(here) begins," third person singular present indicative of incipere "begin" (see incipient).
incise (v.): "to make a cut," 1540s, from French inciser (15c.), from Old French enciser "cut, cut out, slice" (12c.), from Latin incisus, past participle of incidere "to cut into, cut through" (see incision). In geology, of rivers, from 1893. Related: Incised; incising.
incision (n.): late 14c., "a cutting made in surgery," from Old French incision (13c.) and directly from Latin incisionem (nominative incisio) "a cutting into," recorded only in figurative senses, noun of action from past participle stem of incidere "to cut in," from in- "into, in, on, upon" (see in- (2)) + -cidere, comb. form of caedere "to cut" (see -cide). Meaning "act of cutting into" is from early 15c.
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.
incisor (n.): "cutting tooth," 1670s, from Medieval Latin incisor "a cutting tooth," literally "that which cuts into," from Latin incisus, past participle of incidere "to cut into" (see incision). Inscisours as the name of a cutting tool is attested from early 15c. Related: Incisorial.
incite (v.): mid-15c., from Old French inciter, enciter "stir up, excite, instigate" (14c.), from Latin incitare "to put into rapid motion," figuratively "rouse, urge, encourage, stimulate," from in- "into, in, on, upon" (see in- (2)) + citare "move, excite" (see cite). Related: Incited; inciting.
incitement (n.): 1590s, "action of inciting; that which incites," from French incitement (16c.), from Latin incitamentum, from incitare (see incite). Earlier was incitation (early 15c.).
incitive (adj.): "inciting, instigating," 1725; see incite + -ive. Other adjectives that have been used are incitative (c. 1500), incitatory (c. 1600), incitory (1941).
incivility (n.): 1580s, "want of civilized behavior, rudeness;" 1610s, "uncourteous behavior to others," from French incivilité (15c.), from Late Latin incivilitatem (nominative incivilitas), from incivilis "not civil," from in- "not, opposite of" (see in- (1)) + civilis "relating to a citizen, relating to public life, befitting a citizen; popular, affable, courteous" (see civil). Meaning "an act of rudeness" is from 1650s. Incivil "not conducive to common good" is from mid-15c.
incivilization (n.): "lack or loss of civilization," 1793; see in- (1) "not, opposite of" + civilization. Decivilization in the same sense is from 1815.
incivism (n.): "want of good citizenship," in English often with a menacing sense, a word from the French Revolution, 1794, from French incivisme; see in- (1) "not" + civic + -ism.
The words civisme and incivisme came into use during the first French revolution, when an appearance of active devotion to the existing government was the great test of good citizenship, and incivism was regarded a crime. [Century Dictionary]
inclemency (n.): 1550s, from Middle French inclémence and directly from Latin inclementia "rigor, harshness, roughness," from inclemens "harsh, unmerciful" (see inclement).
inclement (adj.): 1660s, from French inclément (16c.) and directly from Latin inclementem (nominative inclemens) "harsh, unmerciful," from in- "not, opposite of, without" (see in- (1)) + clementem "mild, placid." "Limitation to weather is curious" [Weekley].
inclinable (adj.): "amenable, disposed, having a mental bent in a certain direction," mid-15c., from Old French enclinable and directly from Latin inclinabilis, from inclinare (see incline (v.)).
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.
incline (v.): in early use also encline, c. 1300, "to bend or bow toward," from Old French encliner "to lean, bend, bow down," from Latin inclinare "to cause to lean; bend, incline, turn, divert," from in- "into, in, on, upon" (see in- (2)) + clinare "to bend," from PIE *klei-n-, suffixed form of *klei- "to lean" (see lean (v.)). Metaphoric sense of "have a mental disposition toward" is early 15c. in English (but existed in classical Latin). Related: Inclined; inclining.
incline (n.): c. 1600, "mental tendency," from incline (v.). The literal meaning "slant, slope" is attested from 1846 in railroading.
inclined (adj.): c. 1300, "having a mental tendency;" 1540s, "having a physical slope," past-participle adjective from incline (v.).
inclose (v.): alternative form of enclose (q.v.).
inclosure (n.): variant of enclosure preserved in some legal uses. Related: Inclosure.
include (v.): early 15c., "to shut (someone or something) in materially, enclose, imprison, confine," also "to have (something) as a constituent part," from Latin includere "to shut in, enclose, imprison, insert," from in- "in" (see in- (2)) + claudere "to shut" (see close (v.)). The alleged Sam Goldwyn-ism "Include me out" is attested from 1937. Related: Included; including.
inclusion (n.): c. 1600, "act of making a part of," from Latin inclusionem (nominative inclusio) "a shutting up, confinement," noun of action from past participle stem of includere (see include). Meaning "that which is included" is from 1839.
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).
inclusive (adj.): "characterized by including a great deal, leaving little out," c. 1600, from Medieval Latin inclusivus (see inclusive (adv.)). The Middle English adjective was incluse "confined, shut in" (late 14c.). Related: Inclusively; inclusiveness.
incogitable (adj.): "unthinkable, inconceivable," 1520s, from Late Latin incogitabilis "unthinking; unthinkable," from in- "not" (see in- (1)) + cogitabilis "thinkable, conceivable," from stem of cogitare "to think" (see cogitation).
incognito (adj./adv.): 1640s as both adjective ("disguised under an assumed name and character") and adverb ("unknown, with concealed identity"), from Italian incognito "unknown," especially in connection with traveling, from Latin incognitus "unknown, not investigated," from in- "not, opposite of, without" (see in- (1)) + cognitus, past participle of cognoscere "to get to know" (see cognizance). Also as a noun, "an unknown man" (1630s). Feminine form incognita was maintained through 19c. by those scrupulous about Latin. Incog was a common 18c. colloquial abbreviation.
incognizant (adj.): also incognisant, 1826, from in- (1) "not, opposite of" + cognizant. Related: Incognizance.
incoherence (n.): 1610s, "want of coherence in thought or language," from in- (1) "not" + coherence; formed on model of Italian incoerenza. From 1670s in literal sense "want of physical coherence."
incoherency (n.): "want of coherence in thought," 1680s, from incoherent + -cy.
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.
incohesion (n.): 1781; see in- (1) "not, opposite of" + cohesion.
incohesive (adj.): 1826, from in- (1) "not" + cohesive. Related: Incohesively; incohesiveness.
incombustible (adj.): "incapable of being burned or consumed by fire," late 15c., from Old French incombustible (14c.) or directly from Medieval Latin incombustibilis; see in- (1) + combustible. As a noun from 1807. Related: Combustibility.
income (n.): c. 1300, "entrance, arrival," literally "a coming in;" see in (adv.) + come (v.). Perhaps a noun use of the late Old English verb incuman "come in, enter." Meaning "money made through business or labor" (i.e., "that which 'comes in' as payment for work or business") first recorded c. 1600. Compare German einkommen "income," Swedish inkomst. Income tax is from 1790, introduced in Britain during the Napoleonic wars, re-introduced 1842; in U.S. levied by the federal government 1861-72, authorized on a national level in 1913.
incoming (n.): late 14c., "action of coming in," from in (adv.) + verbal noun from come (v.). As a present participle adjective, from 1753. Of game, from 1892; transferred in World War I to artillery; as a warning cry of incoming shellfire, it seems to date to the U.S. war in Vietnam (1968).
incoming (adj.): 1753, "coming in as an occupant," present-participle adjective from in (adv.) + come (v.). Of game, from 1892; transferred in World War I to artillery; as a warning cry of incoming shellfire, it seems to date to the U.S. war in Vietnam (1968).
incommensurability (n.): 1560s, from incommensurable + -ity.
incommensurable (adj.): "having no common measure," 1550s, from Middle French incommensurable (14c.) or directly from Medieval Latin incommensurabilis, from in- "not, opposite of, without" (see in- (1)) + Late Latin commensurabilis, from Latin com- "with" (see com-) + mensurabilis "measurable," from mensurare "to measure" (see measure (v.)). Related: Incommensurably.
incommensurate (adj.): "not of equal measure; not having a common measure," 1640s, from in- (1) "not, opposite of" + commensurate.
incommodious (adj.): 1550s, from in- (1) "not, opposite of" + commodious. Related: Incommodiously. A verb, incommode, is attested from late 16c., from Latin incommodare. The Latin adjective was incommodus "inconvenient."
incommodity (n.): early 15c., from Old French incommodité (14c.), from Latin incommoditas "inconvenience, disadvantage; damage, injury," from incommodus "inconvenient, unsuitable, troublesome," from in- "not" (see in- (1)) + commodus "suitable, convenient" (see commode).
incommunicability (n.): 1630s, from incommunicable + -ity.
incommunicable (adj.): "not able to be communicated," 1570s, from in- (1) "not" + communicable. Earlier in a now-disused sense of "not communicative" (1570s). Related: Incommunicably.