mu-meson(n = noun.object) muon, negative muon - an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino;
an elementary particle with a negative charge and a half-life of 2 microseconds; the muon. It is a lepton, not a true meson, and decays to an electron and neutrino and antineutrino. [WordNet 1.5]