not governed by or according to reason; illogical
not capable of reasoning
of a number: having a value that cannot be expressed exactly as the result of dividing one integer by another: compare is an irrational number
an irrational root of an equation
irrationalism noun
irrationalist noun
irrationality /-ʹnaliti/ noun
irrationally adv
[Middle English from Latin irrationalis, from in-1 + rationalis: see rational1]