Muon
WordNet
noun
(1) An elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino
WiktionaryText
Etymology
Contraction of mu-meson (the particle has now been recategorised as a lepton).
Noun
- An unstable elementary particle in the lepton family, having similar properties to the electron but with a mass 209 times greater.