The name "lepton" comes from the Greek λεπτόν, meaning "small" or "thin". However, this name originates from before the discovery of a particularly heavy lepton called the tauon. The tauon is nearly twice the mass of a proton.
There are 12 known types of lepton, 3 of which are matter particles (the electron, the muon and the tauon), 3 corresponding neutrinos, and their 6 respective antiparticles. All known charged leptons have a single negative or positive electric charge (depending on whether they are particles or antiparticles) and all of the neutrinos and antineutrinos have neutral electric charge. In general, the number of leptons of the same type (electrons and electron neutrinos; muons and muon neutrinos; tauons and tau neutrinos) remains the same when particles interact (known as conservation of lepton number).
Lepton pl. Lepta (Λεπτόν pl. Λεπτά) is the name of various fractional units of currency used in the Greek-speaking world from antiquity until today.
The Roman mite was informally called lepton in the Greek-speaking parts of the Roman Empire; this use is seen in the New Testament.
In modern Greece, lepton (modern form: lepto, Λεπτό) is the name of the 1/100 denomination of all the official currencies of the Greek state: The Phoenix (1827-1832), the Drachma (1832-2001) and the Euro (2002-current).