lepton

¹ American  

[lep-ton] / ˈlɛp tɒn /

noun

plural

lepta

1. an aluminum coin of modern Greece until the euro was adopted, one 100th of a drachma.

2. a small copper or bronze coin of ancient Greece.

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lepton ² American  

[lep-ton] / ˈlɛp tɒn /

noun

Physics.

1. any of a class of particles with spin of ½ that are not subject to the strong force and that are believed to be truly elementary and not composed of quarks or other subunits. The leptons known or believed to exist are the electron and electron-neutrino, the muon and mu-neutrino, and the tau lepton and tau-neutrino.

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lepton ¹ British  

/ ˈlɛptɒn /

noun

1. a former Greek monetary unit worth one hundredth of a drachma

2. a small coin of ancient Greece

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lepton ² British  

/ ˈlɛptɒn /

noun

1. physics any of a group of elementary particles and their antiparticles, such as an electron, muon, or neutrino, that participate in electromagnetic and weak interactions and have a half-integral spin

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lepton Scientific  

/ lĕp′tŏn′ /

1. Any of a family of elementary particles that interact through the weak force and do not participate in the strong force. Leptons include electrons, muons, tau particles, and their respective neutrinos, the electron neutrino, the muon neutrino, and the tau neutrino. The antiparticles of these six particles are also leptons.

2. Compare hadron See Note at elementary particle See Table at subatomic particle

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lepton Cultural  

1. Any one of six elementary particles that are one of the fundamental constituents of matter. Leptons are not affected by the strong force and are not normally found in the nucleus of the atom. The electron and the neutrino are examples of leptons.

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Other Word Forms

• leptonic adjective

Etymology

Origin of lepton¹

First recorded in 1715–25; from Greek leptón (nómisma) “a small (coin),” noun use of neuter of leptós small; see lepto-

Origin of lepton²

1948; < Greek, neuter of leptós small, slight; see lepto-, -on ¹

Example Sentences

Observing such a process would break a fundamental rule of particle physics called lepton flavor conservation, which is a key part of the Standard Model, and would provide direct evidence for physics beyond existing theories.

From Science Daily • Feb. 2, 2026

"Thermal lepton pairs, or electron-positron emissions produced throughout the QGP's lifetime, emerged as ideal candidates," Geurts said.

From Science Daily • Oct. 29, 2025

If they don’t, then they violate lepton flavor universality—and the unexpected g-factor measurement suggested that’s just what was happening.

From Scientific American • Nov. 14, 2022

From then on, the evidence for lepton flavor universality violation has continued to grow.

From Scientific American • Nov. 14, 2022

A lepton is a very small brass Jewish coin worth half a Roman quadrans each, which is worth a quarter of the copper assarion.

From The World English Bible (WEB): Luke by Anonymous