proton

UK: /ˈprəʊtɒn/ US: /ˈproʊtɑn/ ,(prō′ton)

WordReference Random House Learner's Dictionary of American English © 2025

pro•ton /ˈproʊtɑn/   n. [countable]

1. Physics a positively charged particle found in all atomic nuclei:
   The number of protons in an atom equals that element's atomic number.

WordReference Random House Unabridged Dictionary of American English © 2025

pro•ton  (prō′ton), n. [Physics, Chem.]

1. Physics a positively charged elementary particle that is a fundamental constituent of all atomic nuclei. It is the lightest and most stable baryon, having a charge equal in magnitude to that of the electron, a spin of ½, and a mass of 1.673 × 10-²⁷ kg. Symbol: P

• noun, nominal use of Greek prôton, neuter of prôtos first 1915–20

pro•ton′ic, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

proton / ˈprəʊtɒn/ noun

1. a stable, positively charged elementary particle, found in atomic nuclei in numbers equal to the atomic number of the element. It is a baryon with a charge of 1.602176462 × 10^–19 coulomb, a rest mass of 1.672 62159 × 10^–27 kilogram, and spin

Etymology: 20th Century: from Greek prōtos first