lepton (n.) Look up lepton at Dictionary.com
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.