mu·​on·​ium myü-ˈō-nē-əm How to pronounce muonium (audio) -ˈä- How to pronounce muonium (audio)
: a short-lived quasi-atom consisting of an electron and a positive muon

Word History


New Latin

First Known Use

1957, in the meaning defined above

Time Traveler
The first known use of muonium was in 1957

Dictionary Entries Near muonium

Cite this Entry

“Muonium.” Dictionary, Merriam-Webster, Accessed 1 Feb. 2023.

More from Merriam-Webster on muonium

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Fashionable Words

  • dog-sunglasses-scarf
  • Which of these items is named for a deadly weapon?
Name That Thing

You know what it looks like… but what is it called?

Solve today's spelling word game by finding as many words as you can with using just 7 letters. Longer words score more points.

Can you make 12 words with 7 letters?