Definition of irrational
- irrational fears
- an irrational root of an equation
- a length that is irrational
He became irrational as the fever got worse.
She had an irrational fear of cats.
These example sentences are selected automatically from various online news sources to reflect current usage of the word 'irrational.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
First Known Use: 14th centurySee Words from the same year
: not thinking clearly : not able to use reason or good judgment
: not based on reason, good judgment, or clear thinking
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