retardation vs agent

retardation and agent both are nouns.

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

As nouns, agent is a hypernym of retardation; that is, agent is a word with a broader meaning than retardation:

retardation (noun)	agent (noun)
the act of slowing down or falling behind	the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause
a decrease in rate of change	an active and efficient cause; capable of producing a certain effect
lack of normal development of intellectual capacities	a businessman who buys or sells for another in exchange for a commission
any agent that retards or delays or hinders	a representative who acts on behalf of other persons or organizations
the extent to which something is delayed or held back	any agent or representative of a federal agency or bureau
	a substance that exerts some force or effect