Any of a class of six elementary fermions, two in each of the three generations of fundamental fermions (one negatively charged and one neutral), and including the electron, electron neutrino, muon, muon neutrino, tauon, and tauon neutrino, together with their associated antiparticles, the antileptons. Leptons participate in weak interactions, but not strong interactions, and have masses generally less than those of mesons and baryons.
lep·tonic (-tŏnĭk) adj.
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Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.