/ Dictionary / Index R running light: Meaning and Definition of Find definitions for: run'ning light" Pronunciation: [key] any of various lights required to be displayed by a vessel or aircraft operating between sunset and sunrise. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. running knot running martingale Related Content Daily Word Quiz: eureka Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language