/ Dictionary / Index U ultrabasic: Meaning and Definition of Find definitions for: ul•tra•ba•sic Pronunciation: (ul"tru-bā'sik), [key] — adj. (of rocks) containing iron and magnesium, with little or no silica. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ultra ultracentrifuge Related Content Daily Word Quiz: reticent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language