/ Dictionary / Index P positronium: Meaning and Definition of Find definitions for: pos•i•tro•ni•um Pronunciation: (poz"i-trō'nē-um), [key] — n. Physics. a short-lived atomic system consisting of a positron and an electron bound together. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. positron emission tomography posole Related Content Daily Word Quiz: fabricate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language