ass vs rump

ass and rump both are nouns.

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

As nouns, ass and rump are synonyms defined as:

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