# fermion

> English word · Noun · IPA /ˈfɜːmɪɒn/ · frequency rank #89,356

## Definitions
1. Any elementary or composite particle that has half-integer spin and thus obeys Fermi–Dirac statistics and the Pauli exclusion principle (equivalently, a particle for which the wavefunction of any system of identical such particles changes sign whenever two are swapped); a baryon, a lepton or a quark;
2. Any elementary or composite particle that has half-integer spin and thus obeys Fermi–Dirac statistics and the Pauli exclusion principle (equivalently, a particle for which the wavefunction of any system of identical such particles changes sign whenever two are swapped); a baryon, a lepton or a quark;
(slightly more loosely) any such particle or any composite particle composed of fermions.

## Etymology
From Fermi + -on. Named after Italian-American physicist Enrico Fermi. Coined by English physicist Paul Dirac in 1945 in a lecture titled "Developments in Atomic Theory".

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/fermion