Irrational synonyms such as barmy, absurd, and arbitrary. Irrational is an adjective, and its antonyms are rational and logical. Additionally, here are 28 synonyms, related words, and verbs for irrational.
absurd, arbitrary, backasswards, barmy, baseless, crazy, daft, foolish, groundless, idiotic, illogical, implausible, laughable, ludicrous, mad, nonsensical, ridiculous, senseless, silly, stupid, unfounded, unjustifiable, unreasonable, unscientific, unsound, untenable, and wild.