/ Dictionary / Index U uranium dioxide: Meaning and Definition of Find definitions for: ura'nium diox'ide Pronunciation: [key] — Chem. Chem. a black, crystalline compound, UO, insoluble in water, used in nuclear fuel rods, in ceramics, and pigments. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. uranium dating uranium hexafluoride Related Content Daily Word Quiz: fresco Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language