An unstable elementary particle which is a type of lepton, having a mass almost twice that of a proton, a negative charge, and a spin of ½; it decays into hadrons (usually pions) or other leptons, and neutrinos.
Etimoloji (İngilizce)
From tau + -on, tau short for Ancient Greek τρίτος (trítos, “third”), being the third lepton discovered.