/ Dictionary / Index T theirn: Meaning and Definition of Find definitions for: theirn Pronunciation: (ârn), [key] — pron. Nonstandard. theirs. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. their theirs Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language