/ Dictionary / Index I insane: Meaning and Definition of Find definitions for: in•sane Pronunciation: (in-sān'), [key] — adj. not sane; not of sound mind; mentally deranged. of, pertaining to, or characteristic of a person who is mentally deranged: insane actions; an insane asylum. utterly senseless: an insane plan. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: insane (Thesaurus) ins and outs insanitary Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language