The Collaborative International Dictionary of English v.0.48:

Gatepost \Gate"post`\ (g[=a]t"p[=o]st`), n.
   1. A post to which a gate is hung; -- called also swinging
      post or hinging post.
      [1913 Webster]

   2. A post against which a gate closes; -- called also
      shutting post.
      [1913 Webster]

WordNet (r) 3.0 (2006):

swinging post
    n 1: the gatepost on which the gate is hung [syn: hinging
         post, swinging post]