Elementary-particle definition

Any subatomic particle, such as one of the fundamental fermions or gauge bosons, that may be a component of other particles but is not made of components itself.

(particle physics) A subatomic particle that cannot be divided, as a lepton, quark, weakon, or classon: in the past any subatomic particle was thought to be an elementary particle.

Any of the smallest, discrete entities of which the universe is composed, including the quarks, leptons, and gauge bosons, which are not themselves made up of other particles. Most types of elementary particles have mass, though at least one, the photon, does not.