sex act vs ass

sex act and ass both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex act	Yes	No	No	No
ass	Yes	No	No	No

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

sex act: 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

sex act (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