antimatter synonym -antiparticle. Each one of the elementary particles is described by a set of quantum numbers. These are charge, spin, parity, baryon number, lepton number, strangeness etc. The elementary particles also occur in pairs such that the members of the pair have opposite values of quantum numbers. For example electron and positron, proton and anti-proton etc. Positron is called antiparticle of electron, anti-proton is antiparticle of proton and so on. For further details see elementary particles.