agent vs retardant

agent and retardant both are nouns.

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

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

agent (noun)	retardant (noun)
the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause	any agent that retards or delays or hinders
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