Breadcrumb Home > Dictionary > Index M mightn't: Meaning and Definition of Find definitions for: might•n't Pronunciation: (mīt'nt), [key] contraction of might not. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mightily mighty ✖ Related Content Daily Word Quiz: triumphalism Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language