weaken vs weakener

weaken is not a noun while weakener is a noun.

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

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

weaken (verb)	weakener (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