weakener vs weaken

weakener is a noun but weaken is not a noun.

Word	Noun	Adjective	Verb	Adverb
weakener	Yes	No	No	No
weaken	No	No	Yes	No

weakener (noun)	weaken (noun)
that which weakens or causes a loss of strength

weakener (verb)	weaken (verb)
	become weaker
	lessen the strength of
	reduce the level or intensity or size or scope of
	lessen in force or effect
	destroy property or hinder normal operations