*swivel*

n. [ AS. swīfan to move quickly, to remove; akin to Icel. sveifla to whirl, shake, svīfa to ramble, to turn. See Swoop, and cf. Swift a reel, Swift, a. ] 1. (Mech.) A piece, as a ring or hook, attached to another piece by a pin, in such a manner as to permit rotation about the pin as an axis. [ 1913 Webster ]

2. (Mil.) A small piece of ordnance, turning on a point or swivel; -- called also swivel gun. Wilhelm. [ 1913 Webster ]

Swivel bridge, a kind of drawbridge that turns round on a vertical axis; a swing bridge. --
Swivel hook, a hook connected with the iron strap of a pulley block by a swivel joint, for readily taking the turns out of a tackle. --
Swivel joint, a joint, the two pieces composing which turn round, with respect to each other, on a longitudinal pin or axis, as in a chain, to prevent twisting. [ 1913 Webster ]