ˌsəlˈfōnēəm noun
( -s )
Etymology: New Latin, from sulf- + -onium
: a univalent cation H 3 S + or radical H 3 S analogous to oxonium with sulfur in place of oxygen and known especially in the form of organic derivatives (as triethyl- sulfonium iodide) made usually by reaction of an organic sulfide with an alkyl halide — compare -thionium