Subatomic particles or quanta; molecular units.
[Originally from electron, probably from the ending of ion and influenced by Greek on, being.]
An electron is a stable subatomic particle with a negative charge. On its model, -on has become the dominant ending with which to label elementary particles and groups of such particles (for another, see -tron); examples include proton (Greek, neuter of prōtos, first), a particle with a positive electric charge equal to that of an electron; meson (Greek mesos, middle), a particle intermediate in mass between an electron and a proton; baryon (Greek barus, heavy), a particle with a mass equal to or greater than that of a proton.
Names for quanta include photon (Greek phōs, phōt-, light), a particle representing a quantum of light or other electromagnetic radiation; graviton, a hypothetical quantum of gravitational energy, regarded as a particle; phonon (Greek phōnē, sound), a quantum of energy or a quasi-particle associated with a compressional wave such as sound or a vibration of a crystal lattice.
The ending has been adopted in molecular biology for entities regarded as units, such as codon (from code), a sequence of three nucleotides which together form a unit of genetic code in a DNA or RNA molecule; intron (Latin intra, inside), a segment of a DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes; and operon (French opérer, to effect, work), a unit made up of linked genes which is thought to regulate other genes responsible for protein synthesis.