/ Dictionary / Index U ultramafic: Meaning and Definition of Find definitions for: ul•tra•maf•ic Pronunciation: (ul"tru-maf'ik), [key] — adj. Geol. ultrabasic. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ultralight ultramarathon Related Content Daily Word Quiz: inane Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language