/ Dictionary / Index M muonium: Meaning and Definition of Find definitions for: mu•o•ni•um Pronunciation: (my-ō'nē-um), [key] — n. Physics. an electron and a positively charged muon bound together by electrical attraction in the same manner as the electron and proton in a hydrogen atom. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. muon muon-neutrino Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language