An Etymological Dictionary of Astronomy and Astrophysics

1. Suffix used in the names of subatomic particles (electron, proton, neutron, gluon, etc.), quanta (photon, graviton, etc.), and other minimal entities or components.
   
2. Suffix used in the meaning of inert gases (e.g. neon, krypton).

See also: 1) Probably extracted from → ion.
2) From Gk. -on, neuter of -os adj. ending.