ass vs sexual relation

ass and sexual relation both are nouns.

Word	Noun	Adjective	Verb	Adverb
ass	Yes	No	No	No
sexual relation	Yes	No	No	No

As nouns, sexual relation is a hypernym of ass; that is, sexual relation is a word with a broader meaning than ass:

ass: slang for sexual intercourse
sexual relation: sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur

ass (noun)	sexual relation (noun)
slang for sexual intercourse	sexual activity between individuals, especially the insertion of a man's penis into a woman's vagina until orgasm and ejaculation occur
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