prettygoodword

lepton (LEP-ton) - n., any of a family of particles (such as electrons, muons, and neutrinos) that have spin quantum number ½ and that experience no strong forces.

Also, a small Greek coin used in various eras since ancient times, currently used as the Greek name for the eurocent (it had been the name of 1/100 of a drachma before Greece went on the euro), but that's not important for this week. There are six known leptons: electrons, muons, and tauons, and their corresponding flavors of neutrinos, corresponding to the three generations of quarks that make up hadrons. Unlike hadrons, they are, as far as we know, fundamental and not composed of other, smaller particles. Coined in 1947 by Dutch-American physicist Abraham Pais from Ancient Greek leptós, small + -(i)on, charged particle (coined in 1834 by English polymath William Whewell from Ancient Greek ión, going, neuter present participle of eîmi, I go).

(No picture for this, because subatomic.)

---L.