the.com/lepton

means A lepton is a fundamental particle (like the electron, muon, tau, or their neutrinos) that doesn't feel the strong nuclear force, making it one of matter's basic, indivisible building blocks.

from From Greek 'leptos,' meaning small, thin, or fine — the same root sense behind 'leprosy' (thin, scaly skin). Physicists in the mid-20th century borrowed it because the first known leptons, like the electron, were lightweights compared to the hefty protons and neutrons of the atomic nucleus. The name stuck even after a heavyweight lepton, the tau, was discovered weighing in far heavier than a proton — proving the family name describes its aloof behavior more than its actual mass.