The Collaborative International Dictionary of English v.0.48:

Capstan \Cap"stan\, n. [F. cabestan, fr. Sp. cabestrante,
   cabrestante, fr. cabestrar to bind with a halter, fr.
   cabestrohalter, fr. L. capistrum halter, fr. capere to hold
   (see Capacious); or perh. the Spanish is fr. L. caper goat
   + stans, p. pr. of stare to stand; cf. F. ch[`e]vre she-goat,
   also a machine for raising heavy weights.]
   A vertical cleated drum or cylinder, revolving on an upright
   spindle, and surmounted by a drumhead with sockets for bars
   or levers. It is much used, especially on shipboard, for
   moving or raising heavy weights or exerting great power by
   traction upon a rope or cable, passing around the drum. It is
   operated either by steam power or by a number of men walking
   around the capstan, each pushing on the end of a lever fixed
   in its socket. [Sometimes spelt Capstern, but improperly.]
   [1913 Webster]

   Capstan bar, one of the long bars or levers by which the
      capstan is worked; a handspike..

   To pawl the capstan, to drop the pawls so that they will
      catch in the notches of the pawl ring, and prevent the
      capstan from turning back.

   To rig the capstan, to prepare the for use, by putting the
      bars in the sockets.

   To surge the capstan, to slack the tension of the rope or
      cable wound around it.
      [1913 Webster]

WordNet (r) 3.0 (2006):

capstan
    n 1: a windlass rotated in a horizontal plane around a vertical
         axis; used on ships for weighing anchor or raising heavy
         sails