Breadcrumb Home > Dictionary > Index M Matin Luther King Day: Meaning and Definition of Find definitions for: Mar'tin Lu'ther King' Day" Pronunciation: [key] the third Monday in January, a legal holiday in some states of the U.S., commemorating the birthday (Jan. 15) of Martin Luther King, Jr. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Martinique Martinmas ✖ Related Content Daily Word Quiz: guilloche Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language