Online Etymology Dictionary

informality (n.): 1590s, from informal + -ity.
informant (n.): 1660s, "someone or something that supplies information," from Latin informantem (nominative informans), present participle of informare (see inform). Meaning "one who gives information to the authorities, informer" is from 1783. As an adjective from 1890. The older noun was informer.
informatics (n.): 1967, translating Russian informatika (1966), from information; also see -ics.
information (n.): late 14c., "act of informing," from Old French informacion, enformacion "information, advice, instruction," from Latin informationem (nominative informatio) "outline, concept, idea," noun of action from past participle stem of informare (see inform). Meaning "knowledge communicated" is from mid-15c. Information technology attested from 1958. Information revolution from 1969.
informative (adj.): "instructive," late 14c., "formative, shaping, plastic," from Medieval Latin informativus, from Latin informatus, past participle of informare (see inform). Related: Informatively.
informer (n.): late 14c., enfourmer "instructor, teacher," native agent noun from inform and also from Old French enformeor. Meaning "one who gives information against another" (especially in reference to law-breaking) is c.1500.
infotainment (n.): 1983, from info- + entertainment.
infra: prefix, "under, below, further on," from Latin infra (see infra-).
infra dig.: 1824, colloquial abbreviation of Latin infra dignitatem "beneath the dignity of."
infra-: word-forming element from Latin infra (adv., prep.) "below, underneath, beneath; later than, smaller, inferior to," from PIE *ndher "under" (cf. Sanskrit adnah "below," Old English under "under, among;" see under). Opposed to super-. Its use as a prefix was rare in Latin.
infra-red: also infrared, 1881 (noun and adjective), from infra- + red.
infraction (n.) $Look up infraction at Dictionary.com$: mid-15c., "the breaking of an agreement," from Middle French infraction and directly from Latin infractionem (nominative infractio) "a breaking, weakening," noun of action from past participle stem of infringere (see infringe).
infralapsarian: 1731, from infra- + Latin lapsus "a fall" (see lapse (n.)) + ending from unitarian, etc. In reference to the Calvinist doctrine that god's election of some to everlasting life was consequent to his decree to allow the Fall of man, and was thus a remedial measure. Contrasted to supralapsarian, in reference to the belief that He always meant to consign most of mankind to eternal fire and that the decision to create some men to be damned was his first decree. There's also a moderate sublapsarian view. Here the decree to elect those who would believe and leave those who do not believe to damnation also comes after the decree to allow the fall, but the decree to provide salvation for man comes immediately after the decree to elect.
infrasonic (adj.): 1927, from infra- + sonic.
infrastructure (n.): 1887, from French infrastructure (1875); see infra- + structure (n.). The installations that form the basis for any operation or system. Originally in a military sense.
infrequency (n.): c.1600, from Latin infrequentia "a small number, thinness, scantiness," noun of quality from infrequentem (see infrequent). Related: Infrequence (1640s).
infrequent (adj.): 1530s, from Latin infrequentem (nominative infrequens) "occurring seldom, unusual," from in- "not" (see in- (1)) + frequens (see frequent). Related: Infrequently.
infrigidation (n.): early 15c., from Late Latin infrigidationem (nominative infrigidatio), noun of action from infrigidare "to make cold," from in- "in, into" (see in- (2)) + frigidare, from frigidus "cold" (see frigid). Related: infrigidate (v.).
infringe (v.): mid-15c., enfrangen, "to violate," from Latin infringere "to damage, break off, break, bruise," from in- "in" (see in- (2)) + frangere "to break" (see fraction). Meaning of "encroach" first recorded c.1760. Related: Infringed; infringing.
infringement (n.): 1590s, from infringe + -ment.
infundibulum (n.): 1799 in the anatomical sense, from Latin infundibulum, literally "a funnel," from infundere "to pour into" (see infuse) + -bulum, suffix forming names of instruments. In some cases a loan-translation into Latin of Greek khoane "funnel." Related: Infundibular.
infuriate (v.): 1660s, from Italian infuriato, from Medieval Latin infuriatus, past participle of infuriare "to madden," from Latin in furia "in a fury," from ablative of furia (see fury). Related: Infuriated; infuriating; infuriatingly.
infuse (v.): early 15c., "to pour in, introduce, soak," from Latin infusus, past participle of infundere "to pour into," from in- "in" (see in- (2)) + fundere "pour, spread" (see found (2)). Figurative sense of "instill, inspire" first recorded 1520s (infusion in this sense dates from mid-15c.). Related: Infused; infusing.
infusion (n.): c.1400, from Old French infusion (13c.) or directly from Latin infusionem (nominative infusio), noun of action from past participle stem of infundere (see infuse).
ingenious (adj.): early 15c., "intellectual, talented," from Middle French ingénieux "clever, ingenious" (Old French engeignos), from Latin ingeniosus "of good capacity, full of intellect; clever, gifted with genius," from ingenium "innate qualities, ability," literally "that which is inborn," from in- "in" (see in- (2)) + gignere, from PIE *gen- "produce" (see genus). Sense of "skillful, clever at contrivance" first recorded 1540s. In a sense of "crafty, clever, skillful" Middle English had enginous (mid-14c.), from Old French engeignos. Related: Ingeniously; ingeniousness.
ingenue (n.): 1848, from French ingénue "artless girl, especially on the stage," fem. of ingénu "ingenuous, artless, simple" (13c.), from Latin ingenuus (see ingenuous). Italicized in English into 20c.
ingenuity (n.): 1590s, "honor, nobility," from Middle French ingénuité and directly from Latin ingenuitatem (nominative ingenuitas) "condition of a free-born man," figuratively "generosity, noble-mindedness," from ingenuus (see ingenuous). Etymologically, this word belongs to ingenuous, but in 17c. ingenious and ingenuous so often were confused (even by Shakespeare) that ingenuity has acquired the meaning "capacity for invention or construction" (first attested 1640s).
ingenuous (adj.): 1590s, "noble in nature," from Latin ingenuus "with the virtues of freeborn people, of noble character, frank, upright, candid," originally "native, freeborn," from in- "in" (see in- (2)) + gen-, root of gignere "beget, produce" (see genus). Sense of "artless, innocent" is 1670s, via evolution from "high-minded" to "honorably open, straightforward," to "innocently frank." Related: Ingenuously; ingenuousness.
ingest (v.): 1610s, 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.
ingestion (n.): 1610s, from Latin ingestionem (nominative ingestio) "a pouring in," noun of action from past participle stem of ingerere (see ingest).
ingle (n.): "fireplace," c.1500, from Scottish, probably from Gaelic aingeal "fire," of uncertain origin. The vogue for Scottish poetry in late 18c. introduced ingleside, ingle-nook to literary English.
inglorious (adj.): 1570s, from Latin ingloriosus, from in- "not" (see in- (1)) + gloriosus (see glorious). Related: Ingloriously; ingloriousness.
ingoing: also in-going, 1825, from in + going.
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.): 1766, see engrain. Figurative use, of qualities, habits, etc., attested from 1851 (in ingrained). Of dyed carpets, etc., 1766, from in grain.
ingrate (n.): "ungrateful person," 1670s, from earlier adjective meaning "unfriendly" (late 14c.) also "ungrateful, unthankful," from Latin ingratus "unpleasant," also "ungrateful," from in- "not" (see in- (1)) + gratus "pleasing, beloved, dear, agreeable" (see grace). The noun meaning "ungrateful person" dates from 1670s.
ingratiate (v.): 1620s, possibly via 16c. Italian ingraziarsi "to bring (oneself) into favor," from Latin in gratiam "for the favor of," from in "in" (see in- (2)) + gratia "favor, grace" (see grace).
ingratitude (n.): mid-14c., from Old French ingratitude (13c.) and directly from Latin ingratitudinem (nominative ingratitudo), noun of quality from ingratus (see ingrate).
ingredient (n.): early 15c., 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).
ingress (n.): mid-15c., from Latin ingressus "an advance; walking; an entry," from past participle stem of ingredi "to step into, enter" (see ingredient). The verb, sometimes said to be American English, is attested from early 14c.
ingrown (adj.): 1660s, "native, innate," from in + grown. Of nails, "that has grown into the flesh," 1878.
inguinal (adj.): 1680s, from Latin inguinalis "of the groin," from inguen (genitive inguinis) "groin," from PIE *engw- "groin, internal organ" (cf. Greek aden "gland").
inhabit (v.): late 14c., from Old French enhabiter "dwell in" (12c.), from Latin inhabitare "to dwell in," from in- "in" (see in- (2)) + habitare "to dwell," frequentative of habere "hold, have" (see habit). Related: Inhabited; inhabiting.
inhabitable (adj.): a word used in two opposite senses: "not habitable" (late 14c., from in- (1) "not" + habitable) and "capable of being inhabited" (c.1600, from inhabit + -able).
inhabitant (n.): early 15c., from Anglo-French inhabitant, from Latin inhabitantem (nominative inhabitans), present participle of inhabitare (see inhabit). Related: Inhabitants. As an adjective, also from early 15c.
inhalant: 1825 (adj.), c.1830 (n.)., from Latin inhalantem, present participle of inhalare (see inhale).
inhalation (n.): 1620s, noun of action from past participle stem of Latin inhalare (see inhale).
inhale (v.): 1725, "to breathe in," back-formation from inhalation or else from Latin inhalare "breathe upon," from in- "upon" (see in- (2)) + halare "breathe." Related: Inhaled; inhaling. Current sense is because the word was taken as the opposite of exhale. Slang sense of "eat rapidly" is recorded from 1924. As a noun, by 1934. Related: Inhaled; inhaling.
inhance (v.): obsolete form of enhance.
inharmonious (adj.): 1711, from in- (1) "not" + harmonious. Related: Inharmoniously.