Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

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

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

Source : WordNet®

cantle
     n : the back of a saddle seat