rump vs ass

rump and ass both are nouns.

Word	Noun	Adjective	Verb	Adverb
rump	Yes	No	No	No
ass	Yes	No	No	No

As nouns, rump and ass are synonyms defined as:

rump (noun)	ass (noun)
the part of an animal that corresponds to the human buttocks	slang for sexual intercourse
the fleshy part of the human body that you sit on	hardy and sure-footed animal smaller and with longer ears than the horse
fleshy hindquarters; behind the loin and above the round	the fleshy part of the human body that you sit on
	a pompous fool