piece of cake vs walkover

piece of cake and walkover both are nouns.

Word	Noun	Adjective	Verb	Adverb
piece of cake	Yes	No	No	No
walkover	Yes	No	No	No

As nouns, piece of cake and walkover are synonyms defined as:

Other synonyms of piece of cake include breeze, child's play, cinch, duck soup, picnic, pushover, snap.

piece of cake (noun)	walkover (noun)
any undertaking that is easy to do	any undertaking that is easy to do
	backbends combined with handstands