irrational

Từ điển Oxford Advanced Learner 8th

ir·ration·al AW BrE [ɪˈræʃənl] NAmE [ɪˈræʃənl] adjective
not based on, or not using, clear logical thought
Syn: ↑unreasonable
•an irrational fear
•You're being irrational.
Opp: ↑rational
Derived Words: ↑irrationality ▪ ↑irrationally

Word Origin:
late Middle English: from Latin irrationalis, from in- ‘not’ + rationalis (from ratio(n-) ‘reckoning, reason’, from rat- ‘reckoned’, from the verb reri).

Thesaurus:
irrational adj.
•These are just irrational fears.
illogical • • unfounded • • groundless • • unscientific • • unjustified • |formal, sometimes disapproving unwarranted •
Opp: rational
an irrational/illogical fear
sb's fears are unjustified/unwarranted
totally irrational/illogical/unfounded/groundless/unscientific/unjustified/unwarranted
Irrational or illogical? Irrational emphasizes that there is no good reason for sth; illogical suggests that sb has used a false line of reasoning from facts that do not support their reasoning.

Example Bank:
•There was nothing inherently irrational in such a decision.
•These are just irrational fears.
•What is the reason for this seemingly irrational behaviour?
•You're being irrational.