Pronunciation: (prō'ton), [key]
—n. Physics, Chem.
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
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.