piece of ass vs ass

piece of ass and ass both are nouns.

Word	Noun	Adjective	Verb	Adverb
piece of ass	Yes	No	No	No
ass	Yes	No	No	No

As nouns, piece of ass and ass are synonyms defined as:

Other synonyms of piece of ass include fuck, fucking, nookie, nooky, piece of tail, roll in the hay, screw, screwing, shag, shtup.

piece of ass (noun)	ass (noun)
slang for sexual intercourse	slang for sexual intercourse
	hardy and sure-footed animal smaller and with longer ears than the horse
	the fleshy part of the human body that you sit on
	a pompous fool