irrecognition (n.) Look up irrecognition at Dictionary.com
1820, from assimilated form of in- (1) "not, opposite of" + recognition.
irreconcilable (adj.) Look up irreconcilable at Dictionary.com
1590s, from assimilated form of in- (1) "not, opposite of" + reconcilable, if that word is so old. Or perhaps from French irréconcilable (16c.). Related: Irreconcilably. As a noun, "one who refuses reconciliation or compromise" (especially in politics), from 1748.
irreconciliation (n.) Look up irreconciliation at Dictionary.com
1640s, from ir- "not, opposite of" + reconciliation. Irreconcilement in the same sense is from 1737.
irrecoverable (adj.) Look up irrecoverable at Dictionary.com
mid-15c., from Old French irrecovrable (Modern French irrecouvrable), 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 formed 1878 which demanded the annexation of neighboring regions where a part of the population was Italian-speaking (Trieste, South Tyrol, Nice, Corsica, etc.); from Italian Irredentista, from irredenta (Italia) "unredeemed (Italy)," fem. of irredento, from in- "not, opposite of" (see in- (1)) + redento, from Latin redemptus, past participle of redimere (see redemption). 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," literally "incapable of being broken down," 1530s, from French irréfragable (16c.) and directly 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
1722, "that cannot be broken or violated," from assimilated form of in- "not, opposite of" (see in- (1)) + refrangible. Related: Irrefrangibly.
irrefutable (adj.) Look up irrefutable at Dictionary.com
"incapable of being disproved," 1610s, from Late Latin irrefutabilis "irrefutable," from assimilated form of in- "not, opposite of" (see in- (1)) + refutabilis "refutable," from refutare (see refute). Related: Irrefutably; irrefutability.
irregardless (adj.) Look up irregardless at Dictionary.com
an erroneous word that, etymologically, means the opposite of what it is used to express; probably a blend of irrespective and regardless, and perhaps inspired by the colloquial use of the double negative as an emphatic. Attested 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.").
irregular (adj.) Look up irregular at Dictionary.com
late 14c., "not in conformity with Church rules," from Old French irreguler "irregular, incapable, incompetent" (13c., Modern French irrégulier), from Medieval Latin irregularis "not regular," from assimilated form of in- "not, opposite of" (see in- (1)) + Latin regularis "having rules" (see regular (adj.)). General sense of "not conforming to regular rules or principles" is from late 15c. "It expresses the fact of being out of conformity with rule, but implies nothing more with certainty. Yet the word is sometimes used in a sinister sense, as though it were a euphemism for something worse." [Century Dictionary] Meaning "unsymmetrical" is from 1580s. In reference to variable stars, from 1797.
irregular (n.) Look up irregular at Dictionary.com
"one not belonging to a regular body" of any sort, "one not subject to or not conforming with established regulations," 1610s, from irregular (adj.). Main modern sense of "a soldier not of the regular army" is from 1747.
irregularity (n.) Look up irregularity at Dictionary.com
early 14c., "violation of Church rules governing admission to clerical office," from Old French irregularité (14c.) and directly from Medieval Latin irregularitas "irregularity," from irregularis "not regular" (see irregular (adj.)). Meaning "that which is irregular" is from late 15c.; sense of "state of non-conformity to rule" is from 1590s; meaning "want of symmetry" is from 1640s.
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.
It is worth remembering that irrelevant & relieving are the same word; that, presumably, is irrelevant which does not relieve or assist the problem in hand by throwing any light upon it. [Fowler]
irreligion (n.) Look up irreligion at Dictionary.com
1590s, from French irréligion (16c.) or directly 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
"beyond remedy," mid-15c., from Late Latin irremediabilis "incurable," from assimilated form of in- "not, opposite of" (see in- (1)) + remediabilis "that may be healed, curable" (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
"not capable of or subject to removal," 1590s, from assimilated form of in- (1) "not, opposite of" + removable. Related: Irremovably; irremovability.
irreparable (adj.) Look up irreparable at Dictionary.com
early 15c., from Old French irréparable (12c.), from Latin irreparabilis "not to be repaired or recovered," from assimilated form of in- "not, opposite of" (see in- (1)) + reparabilis "that can be repaired" (see repair (v.)). Irrepairable, from the English verb, was used 16c.-17c. but seldom was seen after.
irreparably (adv.) Look up irreparably at Dictionary.com
mid-15c., from irreparable + -ly (2).
irreplaceable (adj.) Look up irreplaceable at Dictionary.com
1806, from assimilated form of in- (1) "not, opposite of" + replaceable. Related: Irreplaceably.
irreprehensible (adj.) Look up irreprehensible at Dictionary.com
"blameless," late 14c., from Late Latin irreprehensibilis, from Latin irreprehensus "blameless, without blame," from assimilated form of in- "not, opposite of" (see in- (1)) + reprehensibilis, from past participle stem of Latin reprehendere "to blame, censure, rebuke; seize, restrain" (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 (n.)). Related: Irreproachably.
irreption (n.) Look up irreption at Dictionary.com
"a creeping in," 1590s, from Late Latin irreptionem (nominative irreptio), noun of action from past participle stem of Latin irrepere, from assimilated form of in- "in" (see in- (2)) + repere "to creep" (see reptile).
irreputable (adj.) Look up irreputable at Dictionary.com
"disreputable," 1709, from assimilated form of in- (1) "not, opposite of" + reputable.
irresistance (n.) Look up irresistance at Dictionary.com
1640s, from assimilated form of in- "not, opposite of" (see in- (1)) + resistance.
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
"not firm in purpose, wavering, given to doubt or hesitation," 1570s, from Latin irresolutus "not loosed, not loosened," 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 assimilated form of in- (1) "not, opposite of" + resolution. Perhaps from or based on French irrésolution (16c.).
irresolvable (adj.) Look up irresolvable at Dictionary.com
1650s, "insoluble," from assimilated form of in- (1) "not, opposite of" + resolvable. Meaning "that cannot be resolved into parts" is from 1785. 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 in its sense of "regardful." Meaning "without taking account of particular circumstances or conditions" had developed by 1690s, from the notion of "not observing or noting with attention." In modern use it tends to be adverbial, in irrespective of, a use attested by c. 1800.
irresponsibility (n.) Look up irresponsibility at Dictionary.com
1767; 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.
irresponsive (adj.) Look up irresponsive at Dictionary.com
"not responsive, not answering," 1797, from assimilated form of in- "not, opposite of" + responsive.
irretractable (adj.) Look up irretractable at Dictionary.com
1744, from assimilated form of in- "not, opposite of" + retractable.
irretrievable (adj.) Look up irretrievable at Dictionary.com
"not recoverable," 1690s (implied in irretrievably), from assimilated form of in- (1) "not, opposite of" + retrievable. Related: Irretrievability.
irreverence (n.) Look up irreverence at Dictionary.com
mid-14c., from Old French irreverence (13c.) or directly 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
"deficient in veneration or respect," mid-15c., from Old French irreverent or directly from Latin irreverentem "disrespectful, irreverent" (see irreverence). Related: Irreverently (early 15c.); irreverential. Irreverend (late 15c.) means "not worthy of respect or veneration."
irreversible (adj.) Look up irreversible at Dictionary.com
1620s, of decrees, etc., "that cannot be overturned or undone," from assimilated form of in- (1) "not, opposite of" + reversible. Of physical things, "that cannot be turned the other way," from 1821. 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
1813, from Latin 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 [Watkins] from PIE *reg- (2) "moist" (see rain (n.)). De Vaan offers as possibilities the root of regere "to direct, lead," on the notion of leading water onto the fields, or to the root of rigere "be stiff," literally "stretch." The first better suits the sense, but has phonetic problems.

Related: Irrigated; irrigating. In Middle English it was an adjective, "watered, flooded" (mid-15c.). Other adjectival forms have been irriguous (1650s), irrigative (1842), irrigatorial (1867).
irrigation (n.) Look up irrigation at Dictionary.com
1610s, "a supplying of water to land," also in medical use, "supply of a liquid to some part of the body," from Latin irrigationem (nominative irrigatio) "a watering, irrigation," noun of action from past participle stem of irrigare "lead water to, irrigate, flood" (see irrigate).
irrisory (adj.) Look up irrisory at Dictionary.com
"given to sneering or laughing derisively at others," 1824, from Late Latin irrisorius "mocking," from irrisor "a mocker," from stem of Latin irridere "to laugh at, make fun of," from assimilated form of in- "in" (see in- (2)) + ridere "to laugh" (see risible). Related: irrision (1520s), from Latin irrisionem, noun of action from the verb.
irritability (n.) Look up irritability at Dictionary.com
1755, from irritable + -ity or else from Latin irribilitas.
irritable (adj.) Look up irritable at Dictionary.com
1660s, "susceptible to mental irritation," from French irritable and directly from Latin irritabilis "easily excited," from irritare "excite, provoke" (see irritate). Meaning "responding quickly to a stimulus" is from 1791. Related: Irritably.