unit of energy commonly used in atomic and nuclear physics, equal to the energy gained by an electron (a charged particle carrying unit electronic charge when the electrical potential at the electron increases by one volt). The electron volt equals 1.602 × 10^-12 erg. The abbreviation MeV indicates 10⁶ (1,000,000) electron volts and GeV, 10⁹ (1,000,000,000).