/ Dictionary / Index S second mate: Meaning and Definition of Find definitions for: sec'ond mate' Pronunciation: [key] the officer of a merchant vessel next in command beneath the first mate. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. secondly secondment Related Content Daily Word Quiz: sinister Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language