The Collaborative International Dictionary of English v.0.48:

Swivel \Swiv"el\, n. [AS. sw[imac]fan to move quickly, to
   remove; akin to Icel. sveifla to whirl, shake, sv[imac]fa 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]

The Collaborative International Dictionary of English v.0.48:

Swivel \Swiv"el\, v. i.
   To swing or turn, as on a pin or pivot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

swivel
    n 1: a coupling (as in a chain) that has one end that turns on a
         headed pin
    v 1: turn on a pivot [syn: pivot, swivel]