irony (n.) Look up irony at Dictionary.com
c.1500, from Latin ironia, from Greek eironeia "dissimulation, assumed ignorance," from eiron "dissembler," perhaps related to eirein "to speak" (see verb). Used in Greek of affected ignorance, especially that of Socrates. For nuances of usage, see humor. Figurative use for "condition opposite to what might be expected; contradictory circumstances" is from 1640s.
irony (adj.) Look up irony at Dictionary.com
"of or resembling iron," late 14c., from iron (n.) + -y (2).
Iroquois Look up Iroquois at Dictionary.com
1660s, from French (c.1600); not an Iroquoian word, perhaps from an Algonquian language. Related: Iroquoian.
irradiance (adj.) Look up irradiance at Dictionary.com
1660s, from irradiant (1520s), from Latin irradiantem (nominative irradians), present participle of irradiare (see irradiate). Related: Irradiancy (1640s).
irradiate (v.) Look up irradiate at Dictionary.com
c.1600, "to cast beams of light upon," from Latin irradiatus, past participle of irradiare "shine forth," from assimilated form of in- "into, in" (see in- (2)) + radiare "to shine" (see radiate). Meaning "expose to radiation other than light" (originally X-rays) is from 1901. Related: Irradiated; irradiating.
irradiation (n.) Look up irradiation at Dictionary.com
1580s, from French irradiation, from Latin *irradiationem, noun of action from past participle stem of irradiare (see irradiate). Originally of light (literally and figuratively); of X-rays, etc., from 1901.
irradicable (adj.) Look up irradicable at Dictionary.com
1728, from ir- "not" + radicable.
irrational (adj.) Look up irrational at Dictionary.com
late 15c., "not endowed with reason" (of beats, etc.); earlier (of quantities) "inexpressible in ordinary numbers" (late 14c.); from Latin irrationalis "without reason," from assimilated form of in- "not, opposite of" (see in- (1)) + rationalis "reason" (see rational). Meaning "illogical, absurd" is attested from 1640s. Related: Irrationally.
irrationality (n.) Look up irrationality at Dictionary.com
1560s, from irrational + -ity.
irreconcilable (adj.) Look up irreconcilable at Dictionary.com
1590s, from French irréconcilable (16c.), from Medieval Latin *irreconcilabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + reconcilabilis (see reconcile). Related: Irreconcilably. As a noun from 1748.
irrecoverable (adj.) Look up irrecoverable at Dictionary.com
mid-15c., from Old French irrecovrable, from assimilated form of in- "not, opposite of" (see in- (1)) + recovrable (see recover). In same sense irrecuperable (from Late Latin irrecuperabilis) is from mid-14c. Related: Irrecoverably.
irredeemable (adj.) Look up irredeemable at Dictionary.com
c.1600, from assimilated form of in- (1) "not, opposite of" + redeemable. Related: Irredeemably.
irredentist (n.) Look up irredentist at Dictionary.com
1882, member of Italian political party which (after 1878) demanded the annexation of neighboring Italian-speaking regions (Trieste, S. Tyrol, Nice, Corsica, etc.), from Italian Irredentista, from (Italia) irredenta "unredeemed (Italy)." Related: Irredentism.
irreducible (adj.) Look up irreducible at Dictionary.com
1530s, from assimilated form of in- (1) "not, opposite of" + reducible. Related: Irreducibly; irreducibility.
irrefragable (adj.) Look up irrefragable at Dictionary.com
"that cannot be refuted," 1530s, from Late Latin irrefragabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin refragari "to oppose, contest," from re- "back" (see re-) + frag-, base of frangere "to break" (see fraction). Related: irrefragably; irrefragability.
irrefrangible (adj.) Look up irrefrangible at Dictionary.com
c.1719, "that cannot be broken," from assimilated form of in- "not, opposite of" (see in- (1)) + refrangible.
irrefutable (adj.) Look up irrefutable at Dictionary.com
1610s, from Latin irrefutabilis "irrefutable," from assimilated form of in- "not, opposite of" (see in- (1)) + refutabilis, from refutare (see refute). Related: Irrefutably; irrefutability.
irregardless Look up irregardless at Dictionary.com
an erroneous word that, etymologically, means the opposite of what it is used to express. Attested in non-standard writing from at least 1870s (e.g. "Portsmouth Times," Portsmouth, Ohio, U.S.A., April 11, 1874: "We supported the six successful candidates for Council in the face of a strong opposition. We were led to do so because we believed every man of them would do his whole duty, irregardless of party, and the columns of this paper for one year has [sic] told what is needed."); probably a blend of irrespective and regardless. Perhaps inspired by the colloquial use of the double negative as an emphatic.
irregular (adj.) Look up irregular at Dictionary.com
late 14c., "not in conformity with Church rules," from Old French irreguler (13c., Modern French irrégulier), from Medieval Latin irregularis, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin regularis (see regular (adj.)). General sense is from late 15c.
irregular (n.) Look up irregular at Dictionary.com
"a soldier not of the regular army," 1747, from irregular (adj.).
irregularity (n.) Look up irregularity at Dictionary.com
early 14c., "violation of Church rules," from Old French irregularité (14c.) and directly from Medieval Latin irregularitas, from irregularis (see irregular). Meaning "state of being not regular" is from 1590s.
irrelevance (n.) Look up irrelevance at Dictionary.com
1735, from irrelevant + -ance. Earlier in the same sense was irrelevancy (1590s).
irrelevant (adj.) Look up irrelevant at Dictionary.com
1680s, from assimilated form of in- (1) "not, opposite of" + relevant. Related: Irrelevantly.
irreligion (n.) Look up irreligion at Dictionary.com
1590s, from Late Latin irreligionem (nominative irreligio) "irreligion, impiety," from assimiliated form of in- "not" (see in- (1)) + religio (see religion).
irreligious (adj.) Look up irreligious at Dictionary.com
c.1400, from Late Latin irreligiosus "irreligious, impious," from assimilated form of in- "not, opposite of" (see in- (1)) + religiosus (see religious). Related: Irreligiously.
irremediable (adj.) Look up irremediable at Dictionary.com
mid-15c., from Late Latin irremediabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + remediabilis (see remediable).
irremediably (adv.) Look up irremediably at Dictionary.com
mid-15c., irremediabili, from irremediable + -ly (2).
irremovable (adj.) Look up irremovable at Dictionary.com
1590s, from ir- "not" + removable. Related: Irremovably; irremovability.
irreparable (adj.) Look up irreparable at Dictionary.com
early 15c., from Old French irréparable (12c.), from Latin irreparabilis "irreparable, irrecoverable," from assimilated form of in- "not, opposite of" (see in- (1)) + reparabilis "that can be repaired" (see repair).
irreparably (adv.) Look up irreparably at Dictionary.com
mid-15c., from irreparable + -ly (2).
irreplaceable (adj.) Look up irreplaceable at Dictionary.com
1807, from assimilated form of in- (1) "not, opposite of" + replaceable. Related: Irreplaceably.
irreprehensible (adj.) Look up irreprehensible at Dictionary.com
late 14c., from Late Latin irreprehensibilis, from assimilated form of in- "not, opposite of" (see in- (1)) + reprehens-, past participle stem of reprehendere (see reprehend).
irrepressible (adj.) Look up irrepressible at Dictionary.com
1767, from assimilated form of in- (1) "not, opposite of" + repressible (see repress).
Increase of population, which is filling the States out to their very borders, together with a new and extended network of railroads and other avenues, and an internal commerce which daily becomes more intimate, is rapidly bringing the States into a higher and more perfect social unity or consolidation. Thus, these antagonistic systems are continually coming into closer contact, and collision results.

Shall I tell you what this collision means? They who think that it is accidental, unnecessary, the work of interested or fanatical agitators, and therefor ephemeral, mistake the case altogether. It is an irrepressible conflict between opposing and enduring forces, and it means that the United States must and will, sooner or later, become either entirely a slaveholding nation, or entirely a free-labor nation. [William H. Seward, speech at Rochester, N.Y., Oct. 2, 1858]
Related: Irrepressibly.
irreproachable (adj.) Look up irreproachable at Dictionary.com
1630s, from French irréprochable (15c.), from assimilated form of in- "not, opposite of" (see in- (1)) + réprochable (see reproach). Related: Irreproachably.
irreputable (adj.) Look up irreputable at Dictionary.com
1709, from assimilated form of in- (1) "not, opposite of" + reputable.
irresistible (adj.) Look up irresistible at Dictionary.com
1590s, from Late Latin irresistibilis, from assimilated form of in- "not, opposite of" (see in- (1)) + resistere (see resist). Related: Irresistibly; irresistibility.
irresolute (adj.) Look up irresolute at Dictionary.com
1570s, from Latin irresolutus, from assimilated form of in- "not, opposite of" (see in- (1)) + resolutus (see resolute). Related: Irresolutely.
irresolution (n.) Look up irresolution at Dictionary.com
1590s, from French irrésolution (16c.), from ir-, assimilated form of in- "not, opposite of" (see in- (1)) + résolution (see resolution).
irresolvable (adj.) Look up irresolvable at Dictionary.com
1650s, from ir- + resolvable. Related: Irresolvably.
irrespective (adj.) Look up irrespective at Dictionary.com
1620s (implied in irrespectively), "disrespectful," from assimilated form of in- (1) "not, opposite of" + respective. Meaning "without taking account of (something)" is from 1690s. Main modern use is adverbial ("irrespective of"), attested from 1839.
irresponsibility (n.) Look up irresponsibility at Dictionary.com
1818; see irresponsible + -ity.
irresponsible (adj.) Look up irresponsible at Dictionary.com
1640s, "not legally answerable for conduct or actions," from assimilated form of in- (1) "not, opposite of" + responsible. Meaning "not acting with a sense of responsibility" is from 1680s. Related: Irresponsibly.
irretrievable (adj.) Look up irretrievable at Dictionary.com
1690s (implied in irretrievably), from assimilated form of in- (1) "not, opposite of" + retrievable (see retrieve). Related: Irretrievably.
irreverence (n.) Look up irreverence at Dictionary.com
mid-14c., from Latin irreverentia "want of reverence, disrespect," from irreverentem (nominative irreverens) "disrespectful, irreverent," from assimilated form of in- "not, opposite of" (see in- (1)) + reverens, present participle of revereri "to stand in awe of" (see revere).
irreverent (adj.) Look up irreverent at Dictionary.com
mid-15c., from Latin irreverentem (see irreverence). Related: Irreverently (early 15c.); irreverential.
irreversible (adj.) Look up irreversible at Dictionary.com
1620s, from assimilated form of in- (1) "not, opposite of" + reversible. Related: Irreversibly.
irrevocable (adj.) Look up irrevocable at Dictionary.com
also irrevokable, late 14c., from Latin irrevocabilis "that cannot be recalled, unalterable," from assimilated form of in- "not, opposite of" (see in- (1)) + revocabilis (see revoke). Related: Irrevocably.
irrigable (adj.) Look up irrigable at Dictionary.com
1844, from stem of irrigate (v.) + -able.
irrigate (v.) Look up irrigate at Dictionary.com
"supply land with water," 1610s, from Latin irrigatus, past participle of irrigare "lead water to, refresh, irrigate, flood," from assimilated form of in- "into, in, on, upon" (see in- (2)) + rigare "to water, to moisten," of uncertain origin, perhaps cognate with rain. Related: Irrigated; irrigating. In Middle English it was an adjective, "watered, flooded" (mid-15c.).
irrigation (n.) Look up irrigation at Dictionary.com
"a supplying of water to land," 1610s, from Latin irrigationem (nominative irrigatio) "a watering," noun of action from past participle stem of irrigare (see irrigate).