/ Dictionary / Index M mayo: Meaning and Definition of Find definitions for: may•o Pronunciation: (mā'ō), [key] — n. Informal. mayonnaise. May•o Pronunciation: (mā'ō), [key] — n. 1865–1939, and his brother1861–1939, U.S. surgeons. a county in NW Connaught province, in the NW Republic of Ireland. 114,548; 2084 sq. mi. (5400 sq. km). Co. seat: Castlebar. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mayo (Thesaurus) mayn't Mayon 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