Not rational; void of reason or understanding; as, brutes are irrational animals.
- Not endowed with reason.
- Affected by loss of usual or normal mental clarity; incoherent, as from shock.
- Marked by a lack of accord with reason or sound judgment: an irrational dislike.
- Being a syllable in Greek and Latin prosody whose length does not fit the metric pattern.
- Being a metric foot containing such a syllable.
- Mathematics Of or relating to an irrational number.
- Mathematics An irrational number.