sexual relation vs ass

sexual relation and ass both are nouns.

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

As nouns, ass is a hyponym of sexual relation; that is, ass is a word with a more specific, narrower meaning than sexual relation:

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: slang for sexual intercourse

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