tet·ra·zo·li·um \ˌ ̷ ̷ ̷ ̷ˈzōlēəm\noun (-s) Etymology: New Latin, from International Scientific Vocabulary tetrazole + New Latin -ium : a univalent ion CH3N4+ or radical CH3N4 analogous to ammonium and derived from tetrazole; also: any of various derivatives of this ion < tetrazolium salts are redox indicators — Science > — compare formazan