The Collaborative International Dictionary of English v.0.48:

Foresail \Fore"sail`\, n. (Naut.)
   (a) The sail bent to the foreyard of a square-rigged vessel,
       being the lowest sail on the foremast.
   (b) The gaff sail set on the foremast of a schooner.
   (c) The fore staysail of a sloop, being the triangular sail
       next forward of the mast.
       [1913 Webster]

WordNet (r) 3.0 (2006):

foresail
    n 1: the lowest sail on the foremast of a square-rigged vessel