The Collaborative International Dictionary of English v.0.48:

Cantle \Can"tle\, n. [OF. cantel, chantel, corner, side, piece,
   F. chanteau a piece cut from a larger piece, dim. of OF. cant
   edge, corner. See 1st Cant.]
   1. A corner or edge of anything; a piece; a fragment; a part.
      "In one cantle of his law." --Milton.
      [1913 Webster]

            Cuts me from the best of all my land
            A huge half moon, a monstrous cantle out. --Shak.
      [1913 Webster]

   2. The upwardly projecting rear part of saddle, opposite to
      the pommel. [Written also cante.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cantle \Can"tle\, v. t.
   To cut in pieces; to cut out from. [Obs.] [Written also
   cantile.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

cantle
    n 1: the back of a saddle seat