lepton

from WordNet (r) 3.0 (2006)

lepton
    n 1: 100 lepta equal 1 drachma in Greece
    2: an elementary particle that participates in weak
       interactions; has a baryon number of 0

from The Collaborative International Dictionary of English v.0.48

lepton \lepton\ n. (Physics)
   an elementary particle that participates in weak interactions
   but does not participate in the strong interaction; it has a
   baryon number of 0. Some known leptons are the {electron},
   the {negative muon}, the {tau-minus particle}, and the
   neutrinos associated with each of these particles.
   [WordNet 1.5 +PJC]