(1):

(n.) A contrivance in some of the ealier steam engines for moving the valves for the alternate admission and shutting off of the steam.

(2):

(n.) An iron instrument having a jaw to fit a nut or the head of a bolt, and used as a lever to turn it with; a wrench; specifically, a wrench for unscrewing or tightening the couplings of hose.

(3):

(n.) One who, or that which, spans.

(4):

(n.) The lock of a fusee or carbine; also, the fusee or carbine itself.