irrational

¹ir·ra·tio·nal

adjective \i-ˈra-sh(ə-)nəl, ˌi(r)-\

Definition of IRRATIONAL

: not rational: as

a (1) : not endowed with reason or understanding (2) : lacking usual or normal mental clarity or coherence

b : not governed by or according to reason <irrational fears>

c Greek & Latin prosody (1) of a syllable : having a quantity other than that required by the meter (2) of a foot : containing such a syllable

d (1) : being an irrational number <an irrational root of an equation> (2) : having a numerical value that is an irrational number <a length that is irrational>

— ir·ra·tio·nal·i·ty \-ˌra-shə-ˈna-lə-tē\ noun

— ir·ra·tio·nal·ly \-ˈra-sh(ə-)nə-lē\ adverb

Examples of IRRATIONAL

1. He became irrational as the fever got worse.
2. She had an irrational fear of cats.

Origin of IRRATIONAL

Middle English, from Latin irrationalis, from in- + rationalis rational

First Known Use: 14th century

Related to IRRATIONAL

Synonyms

fallacious, illegitimate, inconsequent, inconsequential, invalid, illogical, nonrational, unreasonable, unreasoning, unsound, weak

Antonyms

logical, rational, reasonable, sound, valid, well-founded, well-grounded

Related Words

eristic (also eristical), misleading, sophistic (or sophistical), specious; half-baked, ill-advised, misguided, unconsidered, unreasoned; inconsistent; absurd, asinine, foolish, meaningless, nonsensical, preposterous, reasonless, senseless, silly; Kafkaesque, odd, peculiar, strange, surreal, unusual, weird; insane, mad, nutty, wacky (also whacky); disordered, disorganized, rambling, random; unconvincing; inexplicable, unaccountable, unexplainable

Near Antonyms

commonsense, sane, sensible, sober, wise; enlightened, informed, just, justified, reasoned; ordered, organized; clear, cogent, compelling, convincing, credible, persuasive, plausible, satisfying, solid; certain, sure, true; confirmed, corroborated, demonstrated, established, substantiated, validated

²irrational

noun

Definition of IRRATIONAL

1

: an irrational being

2

: irrational number

First Known Use of IRRATIONAL

1646

Rhymes with IRRATIONAL

cross-national, transnational

ir·ra·tio·nal

adjective \(ˈ)ir-ˈ(r)ash-nəl, -ən-^əl\   (Medical Dictionary)

Medical Definition of IRRATIONAL

: not rational: as a : lacking usual or normal mental clarity or coherence <was irrational for several days after the accident> b : not governed by or according to reason <irrational fears>

—ir·ra·tio·nal·i·ty \(ˌ)ir-ˌ(r)ash-ə-ˈnal-ət-ē\ noun, plural ir·ra·tio·nal·i·ties

—ir·ra·tio·nal·ly \(ˈ)ir-ˈ(r)ash-nə-lē, -ən-^əl-ē\ adverb