Tap′pet.
(Machinery.) a. A projecting arm a which is touched by a cam b, or other moving object, in order to impart an intermittent reciprocation to the rod c. Specially used as a valvemotion in steam-engines. b. A similar device on the stem of a stamp in an ore-battery. It is struck by a cam, lifting the stamp, which falls as the cam slides from under the tappet, its shoe striking the ore in the mortar.