The Collaborative International Dictionary of English v.0.48:

Seashore \Sea"shore`\, n.
   1. The coast of the sea; the land that lies adjacent to the
      sea or ocean.
      [1913 Webster]

   2. (Law) All the ground between the ordinary high-water and
      low-water marks.
      [1913 Webster]

WordNet (r) 3.0 (2006):

seashore
    n 1: the shore of a sea or ocean [syn: seashore, coast,
         seacoast, sea-coast]