I. i-ˈra-sh(ə-)nəl, ˌi(r)- adjective
Etymology: Middle English, from Latin irrationalis, from in- + rationalis rational
Date: 14th century
: not rational: as
a.
(1) : not endowed with reason or understanding
(2) : lacking usual or normal mental clarity or coherence
b. : not governed by or according to reason
irrational fears
c. Greek & 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
• ir·ra·tio·nal·i·ty -ˌra-shə-ˈna-lə-tē noun
• ir·ra·tio·nal·ly -ˈra-sh(ə-)nə-lē adverb
II. noun
Date: 1646
1. : an irrational being
2. : irrational number