Definitions

irrational

[ih-rash-uh-nl, -rash-nl] / ɪˈræʃ ə nl, -ˈræʃ nl /

ADJECTIVE

illogical, senseless

Synonyms

STRONGEST

aberrant absurd crazy foolish incoherent insane preposterous ridiculous stupid unreasonable unsound unwise wrong

STRONG

invalid loony raving silly wild

WEAK

brainless cockamamie delirious demented disconnected disjointed distraught fallacious flaky freaky injudicious kooky mad mindless nonsensical nutty off-the-wall reasonless sophistic specious unreasoning unstable unthinking wacky

Antonyms

STRONGEST

balanced logical rational realistic reasonable responsible sane sensible serious smart sound thoughtful well wise

WEAK

reflective stable

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Peter Doomanis backed up Carpenter’s claims against Applegate and said that the man poses a serious “and escalating” threat to the singer, and has “developed a disturbing and irrational fixation” on the pop star.

From Los Angeles Times • Jun. 2, 2026

During periods of irrational exuberance, stock prices tend to rise more quickly than Wall Street’s earnings estimates.

From MarketWatch • May 26, 2026

Macgregor had never known her old friend to be irrational.

From The Wall Street Journal • May 23, 2026

Quantum mania has become a staple of the tech sector, dismissed by some as irrational exuberance.

From Barron's • May 6, 2026

Whenever she wanted something, he had the irrational urge to provide it.

From "The Son of Neptune" by Rick Riordan

Vocabulary lists containing irrational

Pi Day Vocabulary

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The Number System

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Divergent

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