Irrational

Part of speech: adjective (a.)

1. Not rational; void of reason or understanding; as, brutes are irrational animals.

2. Not according to reason; absurd; foolish. It seemed utterly irrational any longer to maintain it. I. Taylor.

3. Not capable of being exactly expressed by an integral number, or by a vulgar fraction; surd; -- said especially of roots. See Surd.

Synonyms: Absurd; foolish; preposterous; unreasonable; senseless. See Absurd.