Main Entry: ¹ir·ra·tio·nal

Pronunciation: \i-ˈra-sh(ə-)nəl, ˌi(r)-\

Function: 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