[′spärk‚ō·vər i¦nish·ē‚ād·əd ′dis‚chärj mə‚shēn·iŋ] (mechanical engineering) An electromachining process in which a potential is impressed between the tool (cathode) and workpiece (anode) which are separated by a dielectric material; a heavy discharge current flows through the ionized path when the applied potential is sufficient to cause rupture of the dielectric.