sexual activity vs suckle

sexual activity is a noun but suckle is not a noun.

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

sexual activity (noun)	suckle (noun)
activities associated with sexual intercourse

sexual activity (verb)	suckle (verb)
	give suck to
	suck milk from the mother's breasts