• (n.) That one of a series of sulphides of any element which has the lowest proportion of sulphur; a sulphide with but one atom of sulphur in the molecule.
Pro`to·sul'phide noun [ Proto- + sulphide .] (Chemistry) That one of a series of sulphides of any element which has the lowest proportion of sulphur; a sulphide with but one atom of sulphur in the molecule.