The Collaborative International Dictionary
Walk-over \Walk"-o`ver\, n. In racing, the going over a course by a horse which has no competitor for the prize.
2. Hence: (colloquially) A one-sided contest; an uncontested, or an easy, victory.
Syn: walk; cake-walk.
Douglas Harper's Etymology Dictionary
"easy victory," 1838, such as one that happens in the absence of competitors, when the solitary starter, being obliged to complete the event, can traverse the course at a walk. Transferred sense of "anything accomplished with great ease" is attested from 1902. To walk (all) over (someone) "treat with contempt" is from 185
Wiktionary
n. 1 A horserace in which only a single horse competes 2 (context by extension English) An uncontested or very easy victory
Usage examples of "walk-over".
A man might rail against the sun's rising in the east as easily as against the Bobcats once again playing the part of the walked-on in the league's latest walk-over -- such were the dull-eyed Facts of Life --but she didn't have to be so mean about it!