sexual activity vs fundament

sexual activity and fundament both are nouns.

Word	Noun	Adjective	Verb	Adverb
sexual activity	Yes	No	No	No
fundament	Yes	No	No	No

sexual activity (noun)	fundament (noun)
activities associated with sexual intercourse	lowest support of a structure
	the fleshy part of the human body that you sit on
	the fundamental assumptions from which something is begun or developed or calculated or explained