sexual activity vs charge up

sexual activity is a noun but charge up is not a noun.

Word	Noun	Adjective	Verb	Adverb
sexual activity	Yes	No	No	No
charge up	No	No	Yes	No

sexual activity (noun)	charge up (noun)
activities associated with sexual intercourse

sexual activity (verb)	charge up (verb)
	cause to be agitated, excited, or roused