lepton (n.)

elementary particle of small mass, 1948, from Greek leptos "small, slight, slender, delicate, subtle," literally "peeled," or "threshed out" (from lepein "to peel," from PIE *lep- (1), a root which yields words for "peel" as well as "small shaving, scale (of a fish)," hence used of things fine, delicate, or weak; see leper) + -on. In Greek it was the name of a small coin, from neuter of leptos. Related: Leptonic.