Definition of: proton

(prō′ton) noun Physics
1. The positively charged nucleus of the atom of the light isotope of hydrogen (symbol, H¹), constituting its principal mass.
2. One of the elementary particles in the nucleus of an atom, having a unitary positive charge and a mass of approximately 1.672 × 10^–24 gram. The atomic number of an element is equivalent to the number of protons in its nucleus. [<NL <Gk. prōton, neut. of prōtos first]