agent vs weakener

agent and weakener both are nouns.

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

As nouns, weakener is a hyponym of agent; that is, weakener is a word with a more specific, narrower meaning than agent:

agent (noun)	weakener (noun)
the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause	that which weakens or causes a loss of strength
an active and efficient cause; capable of producing a certain effect
a businessman who buys or sells for another in exchange for a commission
a representative who acts on behalf of other persons or organizations
any agent or representative of a federal agency or bureau
a substance that exerts some force or effect