muon

n. unstable lepton, tiny particle that can have a negative or positive charge

The muon (from the letter mu (μ)--used to represent it) is an  elementary particle with negative electric charge and a spin of 1/2. It has a mean lifetime of 2.2μs, longer than any other unstable lepton, meson or baryon except for the neutron. Together with the electron, the tau, and the neutrinos, it is classified as a lepton. Like all fundamental particles, the muon has an antimatter partner of opposite charge but equal mass and spin: the antimuon, also called a positive muon. Muons are denoted by μ− and antimuons by μ+.
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Noun
1. an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino
(synonym) negative muon, mu-meson
(hypernym) lepton

n. muon, unstable lepton, tiny particle that can have a negative or positive charge

A heavy cousin of the electron, being a lepton. It has a rest mass 206 times that of an electron, and it (and its positive antiparticle) have a mean life of 2.2 microseconds to decay into an electron (or positron) and a neutrino and an antineutrino. Being a fermion, it has an intrinsic spin quantum number of 1/2. Muons originate from the decay of charged pi-mesons (mean life 0.026 µsec) which are produced in high energy (> 140 MeV) nuclear reactions.