A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.
- ‘Overall, atoms are neutral and the number of protons in their nuclei equals the number of electrons.’
- ‘An alpha particle consists of two protons and two neutrons; it is the nucleus of a helium atom.’
- ‘Its atoms have a nucleus of two protons and two neutrons, orbited by two electrons.’
- ‘The matter was composed primarily of an ionized gas of electrons, protons, and helium nuclei.’
- ‘The strong force also attracts protons to protons or neutrons to neutrons.’
1920s: from Greek, neuter of prōtos first.