sex activity vs siren

sex activity and siren both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex activity	Yes	No	No	No
siren	Yes	No	No	No

sex activity (noun)	siren (noun)
activities associated with sexual intercourse	eellike aquatic North American salamander with small forelimbs and no hind limbs; have permanent external gills
	an acoustic device producing a loud often wailing sound as a signal or warning
	a warning signal that is a loud wailing sound
	a woman who is considered to be dangerously seductive