onium

In chem., a termination given to the names of compound radicals which are analogous in structure and chemical function to ammonium, NH₄, as phosphonium, PH₄, or tetramethylphosphonium, P (CH₃)₄.

any cation derived by the addition of a proton to the hydride of any element of the nitrogen, chalcogen or halogen families

any organic derivative of these compounds

the bound pair of a particle and its antiparticle