/ Dictionary / Index D deuterium: Meaning and Definition of Find definitions for: deu•te•ri•um Pronunciation: (d-tēr'ē-um, dy-), [key] — n. Chem. an isotope of hydrogen, having twice the mass of ordinary hydrogen; heavy hydrogen. Symbol: D; at. wt.: 2.01; at. no.: 1. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: deuterium (Thesaurus) deuteride deuterium oxide Related Content Daily Word Quiz: reclusive Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language