/ Dictionary / Index T third mate: Meaning and Definition of Find definitions for: third' mate' Pronunciation: [key] the officer of a merchant vessel next in command beneath the second mate. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. third man Third Order Related Content Daily Word Quiz: endear Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language