infecund (adj.) Look up infecund at Dictionary.com
early 15c., from Latin infecundus, from in- "not, opposite of" (see in- (1)) + fecundus (see fecund). Related: Infecundity.
infelicitous (adj.) Look up infelicitous at Dictionary.com
"unhappy, unlucky," 1754, from in- (1) "not, opposite of" + felicitous. Earlier was infelicious (1590s). Related: infelicitously; infelicitousness.
infelicity (n.) Look up infelicity at Dictionary.com
late 14c., "unhappiness," from Latin infelicitas "bad luck, misfortune, unhappiness," from infelix (genitive infelicis) "unfruitful, barren; unfortunate, unhappy; causing misfortune, unlucky," from in- "not, opposite of" (see in- (1)) + felix (see felicity). Meaning "inappropriateness, unhappiness as to occasion" is from 1610s.
infer (v.) Look up infer at Dictionary.com
in logic, "to 'bring in' as a conclusion of a process of reasoning," 1520s, from Latin inferre "bring into, carry in; deduce, infer, conclude, draw an inference; bring against," from in- "in" (see in- (2)) + ferre "carry, bear," from PIE *bher- (1) "to bear, to carry, to take" (cognates: Sanskrit bharati "carries;" Avestan baraiti "carries;" Old Persian barantiy "they carry;" Armenian berem "I carry;" Greek pherein "to carry;" Old Irish beru/berim "I catch, I bring forth;" Gothic bairan "to carry;" Old English and Old High German beran, Old Norse bera "barrow;" Old Church Slavonic birati "to take;" Russian brat' "to take," bremya "a burden").

General sense of "draw a conclusion" is first attested 1520s; intransitive sense is from 1570s.
inference (n.) Look up inference at Dictionary.com
1590s, "action of inferring;" 1610s, "that which is inferred;" from Medieval Latin inferentia, from Latin inferentem (nominative inferens), present participle of inferre "bring into; conclude, deduce" (see infer).
inferential (adj.) Look up inferential at Dictionary.com
1650s, from Medieval Latin inferentia (see inference) + -al (1). Related: Inferentially.
inferior (n.) Look up inferior at Dictionary.com
"person inferior to another in rank, etc.," early 15c., from inferior (adj.).
inferior (adj.) Look up inferior at Dictionary.com
early 15c., of land, "low, lower down, lower in position," from Latin inferior "lower, further down" (also used figuratively), comparative of inferus (adj.) "that is below or beneath," from infra "below" (see infra-). Meaning "lower in degree, rank, grade, or importance" is from 1530s; absolutely, "of low quality or rank," also from 1530s.
inferiority (n.) Look up inferiority at Dictionary.com
"state of being inferior," 1590s, probably from Medieval Latin *inferioritas; see inferior + -ity. Inferiority complex first attested 1919.
The surrender of life is nothing to sinking down into acknowledgment of inferiority. [John C. Calhoun]
infernal (adj.) Look up infernal at Dictionary.com
late 14c., "of or pertaining to the underworld," (ancient Tartarus, the sunless abode of the dead, or the Christian Hell), from Old French enfernal, infernal "of Hell, hellish" (12c.), from Late Latin infernalis "of or belonging to the lower regions," from infernus "hell" (Ambrose), in classical Latin "the lower (world)," noun use of infernus "lower, lying beneath, underground, of the lower regions," from infra "below" (see infra-).

Pluto was infernus rex, and Latin inferi meant "the inhabitants of the infernal regions, the dead." Association of the word with fire and heat is via the Christian conception of Hell. Meaning "devilish, hateful" is from early 15c.; meaning "suitable for or appropriate to Hell" is from c. 1600. As a name of Hell, or a word for things which resemble it, the Italian form inferno has been used in English since 1834, via Dante. Related: Infernally.
inferno (n.) Look up inferno at Dictionary.com
1834, "Hell, the infernal regions," from Italian inferno, from Late Latin infernus "Hell," in classical Latin "the lower world" (see infernal). As "a large, raging fire" from 1928.
infertile (adj.) Look up infertile at Dictionary.com
1590s, from French infertile (15c.), from Late Latin infertilis "unfruitful," from in- "not, opposite of" (see in- (1)) + Latin fertilis "fruitful, productive" (see fertile).
infertility (n.) Look up infertility at Dictionary.com
c. 1600, from French infertilité (16c.) or directly from Late Latin infertilitatem (nominative infertilitas), from infertilis "not fertile, unfruitful" (see infertile).
infest (v.) Look up infest at Dictionary.com
late 15c., "to attack, assail, hurt, distress, annoy," from Old French infester (14c.), from Latin infestare "to attack, disturb, trouble," from infestus "unsafe, hostile, threatening, dangerous," originally "inexorable, not able to be handled," from in- "not, opposite of" (see in- (1)) + -festus "(able to be) seized." Sense of "swarm over in large numbers, attack parasitically" first recorded c. 1600. Related: Infested; infesting.
infestation (n.) Look up infestation at Dictionary.com
early 15c., "a being infested," from Old French infestacion, from Late Latin infestationem (nominative infestatio) "a troubling, a disturbing, a molesting," noun of action from past participle stem of Latin infestare "to attack, disturb" (see infest).
infibulate (v.) Look up infibulate at Dictionary.com
"to clasp, confine with a buckle, ring, clasp, or the like," especially of the sexual organs, to prevent copulation, 1620s, from Latin infibulatus, past participle of infibulare "to close with a clasp," from in- "on" (see in- (2)) + fibula "a clasp, pin" (see fibula). Related: Infibulated.
This operation was very generally practised in antiquity upon both young men and young women, but in later times chiefly upon the latter; and it is said to be still in use in some parts of the East. [Century Dictionary, 1902]
infibulation (n.) Look up infibulation at Dictionary.com
1640s, noun of action from infibulate (q.v.); perhaps from or modeled on French infibulation or Medieval Latin *infibulatio.
infidel (n.) Look up infidel at Dictionary.com
mid-15c., "adherent of a religion opposed to Christianity," from Middle French infidèle, from Latin infidelis "unfaithful, not to be trusted," in Late Latin "unbelieving" (in Medieval Latin also as a noun, "unbeliever"), from in- "not, opposite of" (see in- (1)) + fidelis "faithful" (see fidelity).

Originally "a non-Christian" (especially a Saracen); later "one who does not believe in religion, disbeliever in religion generally" (1520s). Also used to translate Arabic qafir (see kaffir), which is from a root meaning "to disbelieve, to deny," strictly referring to all non-Muslims but virtually synonymous with "Christian;" hence, from a Muslim or Jewish point of view, "a Christian" (1530s). As an adjective from mid-15c., "of a religion opposed to Christianity;" 1520s as "rejecting the Christian religion while accepting no other."
infidelity (n.) Look up infidelity at Dictionary.com
c. 1400, "want of faith, unbelief in religion; false belief, paganism;" also (early 15c.) "unfaithfulness or disloyalty to a person" (originally to a sovereign, by 16c. to a lover or spouse), from French infidélité (12c.) or directly from Latin infidelitatem (nominative infidelitas) "unfaithfulness, faithlessness," noun of quality from infidelis "unfaithful, unbelieving" (see infidel).
infield (n.) Look up infield at Dictionary.com
1733, "land of a farm which lies nearest the homestead," from in (adv.) + field (n.). Baseball diamond sense first attested 1866. Related: Infielder (1867).
infiltrate (v.) Look up infiltrate at Dictionary.com
1758, of fluids, from in- (2) "in" + filtrate (v.). Perhaps modeled on French infiltrer (16c.). Military sense of "penetrate enemy lines" attested from 1934. Related: Infiltrated; infiltrating.
infiltration (n.) Look up infiltration at Dictionary.com
"action or process of infiltrating," in physics, 1796, noun of action from infiltrate. Figurative sense of "a passing into" (anything immaterial) is from 1840; military sense of "stealthy penetration of enemy lines" dates from 1930. The same word had been used earlier in a medical sense of "a knitting together" (early 15c.), from Medieval Latin infiltratio.
infinite (adj.) Look up infinite at Dictionary.com
late 14c., "eternal, limitless," also "extremely great in number," from Old French infinit "endless, boundless" and directly from Latin infinitus "unbounded, unlimited, countless, numberless," from in- "not, opposite of" (see in- (1)) + finitus "defining, definite," from finis "end" (see finish (v.)). The noun meaning "that which is infinite" is from 1580s.
infinitely (adv.) Look up infinitely at Dictionary.com
early 15c., from infinite + -ly (2).
infinitesimal (adj.) Look up infinitesimal at Dictionary.com
1710 (1650s as a noun), "infinitely small, less than any assignable quantity," from Modern Latin infinitesimus, from Latin infinitus "infinite" (see infinite) + ordinal word-forming element -esimus, as in centesimus "hundredth." Related: Infinitesimally.
infinitive (n.) Look up infinitive at Dictionary.com
"simple, uninflected form of a verb, expressing its general sense," 1510s, from earlier use as an adjective (mid-15c.), from Late Latin infinitivus "unlimited, indefinite," from Latin infinitus "not limited" (see infinite). "Indefinite" because not restricted by person or number. Related: Infinitival; infinitively.
infinitude (n.) Look up infinitude at Dictionary.com
1640s, from Medieval Latin *infinitudo, from Latin infinitus (see infinite) on model of multitudo, magnitudo. Or the English word is perhaps from or modeled on French infinitude (1610s).
infinity (n.) Look up infinity at Dictionary.com
late 14c., from Old French infinité "infinity; very large number or quantity" (13c.), from Latin infinitatem (nominative infinitas) "boundlessness, endlessness," from infinitus boundless, unlimited" (see infinite). Latin infinitas was used as a loan-translation of Greek apeiria "infinity," from apeiros "endless."
infirm (adj.) Look up infirm at Dictionary.com
late 14c., "weak, unsound" (of things), from Latin infirmus "weak, frail, feeble, not strong or firm" (figuratively "superstitious, pusillanimous, inconstant"), from in- "not, opposite of" (see in- (1)) + firmus "strong; stable," figuratively "constant, trusty" (see firm (adj.)). Of persons, "not strong, unhealthy," first recorded c. 1600. As a noun from 1711.
infirmary (n.) Look up infirmary at Dictionary.com
mid-15c., "sick bay in a monastery," formerly also enfermerie, also firmary, fermery, from Old French enfermerie "hospital" and directly from Medieval Latin infirmaria "a place for the infirm," from Latin infirmus "weak, frail," (see infirm). According to OED, the common name for a public hospital in 18c. England.
infirmity (n.) Look up infirmity at Dictionary.com
late 14c., "disease, sickness; lack of capability, weakness," from Latin infirmitatem (nominative infirmitas) "want of strength, weakness, feebleness," also "the weaker sex" [Lewis], noun of quality from infirmus "weak, frail" (see infirm). Perhaps in part from Middle French infirmité, Old French enfermete "illness, sickness, disease; moral weakness."
inflame (v.) Look up inflame at Dictionary.com
mid-14c., "make (someone) ardent; set (the spirit, etc.) on fire" with a passion or religious virtue, a figurative sense, from Old French enflamer "catch fire; set on fire" (Modern French enflammer), from Latin inflammare "to set on fire, kindle," figuratively "to rouse, excite," from in- "in" (see in- (2)) + flammare "to flame," from flamma "a flame" (see flame (n.)).

The literal sense of "to cause to burn" first recorded in English late 14c. Meaning "to heat, make hot, cause inflammation" is from 1520s. Formerly also enflame, but since 16c. the spelling with in- has predominated. Related: Inflamed; Inflaming.
inflammable (adj.) Look up inflammable at Dictionary.com
"able to be set alight," c. 1600, from Middle French inflammable, from Medieval Latin inflammabilis, from Latin inflammare "to set on fire" (see inflame).Since 1980s use of the word, especially in safety warnings, has been sometimes discouraged for fear it could be misunderstood as meaning "non-flammable" through confusion of the two prefixes in-. The word was used earlier in medicine in the sense "liable to inflammation" (early 15c.). Related: Inflammability.
inflammation (n.) Look up inflammation at Dictionary.com
early 15c., in pathology, "excessive redness or swelling in a body part," from Old French inflammation (14c.) and directly from Latin inflammationem (nominative inflammatio) "a kindling, a setting on fire," noun of action from past participle stem of inflammare "to set on fire" (see inflame). Literal sense "act of setting on fire" in English is from 1560s.
inflammatory (adj.) Look up inflammatory at Dictionary.com
"tending to rouse passions or desires," 1711, a figurative use from Latin inflammat-, past participle stem of inflammare "to set on fire" (see inflame) + -ory. From 1732 in pathology, "accompanied by (pathological) inflammation." as a noun from 1680s.
inflatable (adj.) Look up inflatable at Dictionary.com
1821, from inflate + -able.
inflate (v.) Look up inflate at Dictionary.com
early 15c., "cause to swell," from Latin inflatus (source also of Italian enfiare, Spanish inflar, French enfler), past participle of inflare "to blow into, inflate" (see inflation). Economics sense (of prices, currency, etc.) is from 1843. In some senses a back-formation from inflation. Related: Inflated; inflating.
inflation (n.) Look up inflation at Dictionary.com
mid-14c., "swelling caused by gathering of 'wind' in the body; flatulence," also, figuratively, "outbursts of pride," from Latin inflationem (nominative inflatio) "a puffing up, a blowing into; flatulence," noun of action from past participle stem of inflare "blow into, puff up," figuratively "inspire, encourage," from in- "into" (see in- (2)) + flare "to blow" (see blow (v.1)).

Meaning "action of inflating with air or gas" is from c. 1600. Monetary sense of "enlargement of prices" (originally by an increase in the amount of money in circulation) first recorded 1838 in American English.
inflationary (adj.) Look up inflationary at Dictionary.com
1916, from inflation + -ary.
inflect (v.) Look up inflect at Dictionary.com
early 15c., "to bend inward," from Latin inflectere (past participle inflexus) "to bend in, bow, curve," figuratively, "to change, alter, influence," from in- "in" (see in- (1)) + flectere "to bend" (see flexible). Grammatical sense "to vary by change of form" (especially at the end of a word) is fromd 1660s. Related: Inflected; inflecting.
inflected (adj.) Look up inflected at Dictionary.com
1640s, "bent, curved," past-participle adjective from inflect (v.). Grammatical sense is from 1775.
inflection (n.) Look up inflection at Dictionary.com
also inflexion, early 15c., from Middle French inflexion and directly from Latin inflexionem (nominative inflexio) "a bending, inflection, modification," noun of action from past participle stem of inflectere "to bend in, to change" (see inflect). For spelling, see connection. Grammatical sense "variation by declension or conjugation" is from 1660s; pronunciation sense "modulation of the voice" is from c. 1600.
inflexibility (n.) Look up inflexibility at Dictionary.com
1610s, from inflexible + -ity.
inflexible (adj.) Look up inflexible at Dictionary.com
late 14c., "incapable of being bent, physically rigid," also figuratively, "unyielding in temper or purpose," from Middle French inflexible and directly from Latin inflexibilis "that cannot be bent," from in- "not, opposite of" (see in- (1) + flexibilis "pliant, yielding" (see flexible). In early 15c. an identical word had an opposite sense, "capable of being swayed or moved," from in- "in, on." Related: Inflexibly.
inflexion (n.) Look up inflexion at Dictionary.com
see inflection; also see -xion. Related: Inflexional.
inflict (v.) Look up inflict at Dictionary.com
1560s, "assail, trouble;" 1590s, "lay or impose as something that must be suffered," from Latin inflictus, past participle of infligere "to strike or dash against; inflict," from in- "in" (see in- (2)) + fligere (past participle flictus) "to dash, strike" (see afflict). You inflict trouble on someone; you afflict someone with trouble. Shame on you.
infliction (n.) Look up infliction at Dictionary.com
1530s, "act of inflicting;" 1580s, "that which is inflicted," from Middle French infliction (15c.), or directly from Late Latin inflictionem (nominative inflictio) "an inflicting, a striking against," noun of action from past participle stem of Latin infligere "to strike or dash against" (see inflict).
inflorescence (n.) Look up inflorescence at Dictionary.com
1760, "arrangement of flowers on a stem in relation to one another," from Modern Latin inflorescentia, from Late Latin inflorescentem (nominative inflorescens) "flowering," present participle of Latin inflorescere "to come to flower," from in- "in" (see in- (2)) + florescere "to begin to bloom" (see flourish (v.)). Meaning "a beginning to bloom" in English is from 1800.
inflow (n.) Look up inflow at Dictionary.com
1839, from in (adj.) + flow (n.).
influence (v.) Look up influence at Dictionary.com
1650s, from influence (n.). Related: Influenced; influencing.