The Collaborative International Dictionary of English v.0.48:

Bitts \Bitts\, n. pl. [Cf. F. bitte, Icel. biti, a beam. ?87.]
   (Naut.)
   A frame of two strong timbers fixed perpendicularly in the
   fore part of a ship, on which to fasten the cables as the
   ship rides at anchor, or in warping. Other bitts are used for
   belaying (belaying bitts), for sustaining the windlass
   (carrick bitts, winch bitts, or windlass bitts), to hold the
   pawls of the windlass (pawl bitts) etc.
   [1913 Webster]