n (mechanics) A rigid piece which is capable of turning about one point, or axis (the fulcrum), and in which are two or more other points where forces are applied; — used for transmitting and modifying force and motion.
n A small such piece to trigger or control a mechanical device (like a button)
n (mechanics) A bar, as a capstan bar, applied to a rotatory piece to turn it.
n (mechanics) An arm on a rock shaft, to give motion to the shaft or to obtain motion from it.