sexual activity vs tail end

sexual activity and tail end both are nouns.

Word	Noun	Adjective	Verb	Adverb
sexual activity	Yes	No	No	No
tail end	Yes	No	No	No

sexual activity (noun)	tail end (noun)
activities associated with sexual intercourse	the fleshy part of the human body that you sit on
	any projection that resembles the tail of an animal
	the time of the last part of something