a(1) : lacking usual or normal mental clarity or coherence
(2) : not endowed with reason or understanding
b : not governed by or according to reason c Greek and Latin prosody
(1) of a syllable : having a quantity other than that required by the meter
(2) of a foot : containing such a syllable
d(1) : being an irrational number an irrational root of an equation (2) : having a numerical value that is an irrational number a length that is irrational