/ Dictionary / Index U uraninite: Meaning and Definition of Find definitions for: u•ran•i•nite Pronunciation: (yoo-ran'u-nīt", -rā'nu-), [key] — n. a mineral, probably originally uranium dioxide, UO, but altered by radioactive decay, and usually containing uranium trioxide, lead, radium, and helium, occurring in several varieties, including pitchblende: the most important ore of uranium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: uraninite (Thesaurus) uranic oxide uraniscus Related Content Daily Word Quiz: magnanimous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language