1.NounThe antiparticle of a lepton."When a W boson decays into a positron and a neutrino, lepton number is conserved because the W boson is a non-lepton, the neutrino is a lepton, and the positron is an antilepton. Likewise, when a W boson decays into an electron and an antineutrino, lepton number is conserved because the W boson is a non-lepton, the electron is a lepton, and the antineutrino is an antilepton."