/ Dictionary / Index U unmerciful: Meaning and Definition of Find definitions for: un•mer•ci•ful Pronunciation: (un-mûr'si-ful), [key] — adj. merciless; relentless; severe; cruel; pitiless. unsparingly great, extreme, or excessive, as amounts: to talk for an unmerciful length of time. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: unmerciful (Thesaurus) unmentionable unmeritable Related Content Daily Word Quiz: rustic Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language