Lepton
From Memory Alpha, the free Star Trek reference.
The leptons are a class of elementary particles, which includes the electron, muon and tau particles, as well as three types of neutrino. For each lepton, there is a corresponding antimatter counterpart known as an antilepton. (DS9: "Emissary")
The name lepton comes from the Greek word "λεπτός" meaning "small", "thin" or "delicate".
Lepton fluctuations are associated with some types of spatial anomalies including wormholes. (TNG: "The Price")
