The Collaborative International Dictionary of English v.0.48:

Walk-over \Walk"-o`ver\, n.
   In racing, the going over a course by a horse which has no
   competitor for the prize.
   [1913 Webster]

   2. Hence: (colloquially) A one-sided contest; an uncontested,
      or an easy, victory.

   Syn: walk; cake-walk.
        [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

walkover
    n 1: backbends combined with handstands
    2: any undertaking that is easy to do; "marketing this product
       will be no picnic" [syn: cinch, breeze, picnic, snap,
       duck soup, child's play, pushover, walkover, piece
       of cake]