sicken vs decline

sicken is not a noun while decline is a noun.

Word	Noun	Adjective	Verb	Adverb
sicken	No	No	Yes	No
decline	Yes	No	Yes	No

As verbs, decline is a hypernym of sicken; that is, decline is a word with a broader meaning than sicken:

Other hypernyms of sicken include worsen.

sicken (noun)	decline (noun)
	a downward slope or bend
	a gradual decrease; as of stored charge or current
	change toward something smaller or lower
	a condition inferior to an earlier condition; a gradual falling off from a better state; decline

sicken (verb)	decline (verb)
get sick	grow smaller
make sick or ill	grow worse
cause aversion in; offend the moral sense of	show unwillingness towards
upset and make nauseated	inflect for number, gender, case, etc.
	go down
	fall in value
	not accept as true