Unreasonable, groundless, unfounded, unsound, ridiculous, silly, senseless, laughable, stupid, untenable, unscientific, crazy, barmy, backasswards, illogical, baseless, unjustifiable, absurd, ludicrous, foolish, nonsensical, idiotic, wild, implausible, arbitrary, mad, and daft.
Example Sentences of Irrational
She made an irrational decision in the heat of the moment.
He had an irrational hatred for the color blue.
He gave an irrational response to a simple question.
The plan was rejected due to its irrational risks.
It’s irrational to expect perfect results every time.
His fear of harmless insects is completely irrational.
It's irrational to panic over something so small.
He often acts in irrational ways under stress.
Her irrational jealousy caused problems in the relationship.
The argument was based on irrational beliefs.