/ Dictionary / Index I irrationalism: Meaning and Definition of Find definitions for: ir•ra•tion•al•ism Pronunciation: (i-rash'u-nl-iz"um), [key] — n. irrationality in thought or action. an attitude or belief having a nonrational basis. a theory that nonrational forces govern the universe. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. irrational irrationality Related Content Daily Word Quiz: acquiesce Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language