An Etymological Dictionary of Astronomy and Astrophysics

A particle of the hadron family which is one of the two particles that make up atomic nuclei. It has an electric charge of one positive fundamental unit,
a diameter of about 1.65 x 10^-13 cm, and a mass of about 1.67 x 10^-24 g
(about 938 MeV c^-2).

See also: From Gk. proton, neuter of protos “first.” Coined by Eng. physicist Ernest Rutherford (1871-1937).