The Collaborative International Dictionary of English v.0.48:

Belaying pin \Be*lay"ing pin`\ (b[-e]*l[=a]"[i^]ng p[i^]n`).
   (Naut.)
   A strong pin in the side of a vessel, or by the mast, round
   which ropes are wound when they are fastened or belayed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

belaying pin
    n 1: a wood or metal bar to which a rope can be secured (as on a
         ship or in mountain climbing)