/an"tee pahr'ti keuhl, an"tuy-/ , n. Physics.
a particle all of whose properties, as mass, spin, or charge, have the same magnitude as but, where appropriate, the opposite sign of a specific elementary particle; neutral pions, photons, and gravitons are considered to be their own antiparticles: The positron is the antiparticle of the electron. Cf. antimatter, annihilation (def. 3).
[ 1930-35; ANTI- + PARTICLE ]