irrational
UK[ɪˈræʃənəl]US[ɪˈræʃənəl]
adj
not based on logical reason or clear thinking
adj
(mathematics) (of a number, etc.) that cannot be expressed as a ratio of two whole numbers
Morpheme Breakdown
ir
rational
ir
not
rational
logical
Etymology
the word 'irrational' is a direct negation of 'rational', formed by adding the latin negative prefix 'ir-' (a variant of 'in-') before the adjective. 'rational' itself stems from latin 'ratio', meaning 'reckoning, reason, or calculation', which derives from the verb 'reri' ('to think, judge'). the core concept of 'ratio' as a proportional relationship evolved into the broader sense of logical reasoning. therefore, 'irrational' literally means 'not endowed with reason', a meaning that has extended from describing illogical human thought to defining numbers that cannot be expressed as a simple ratio.
Analysis
Structure: ir (not) + rational (logical)
ir- (prefix, latin origin, meaning 'not'); rational (adjective, latin origin, from 'rationalis', meaning 'logical, based on reason')
Examples
his fear of flying was completely irrational.
she made an irrational decision in the heat of the moment.
the square root of two is an irrational number.