substance vs agent

substance and agent both are nouns.

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

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

substance (noun)	agent (noun)
the real physical matter of which a person or thing consists	the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause
a particular kind or species of matter with uniform properties	an active and efficient cause; capable of producing a certain effect
the property of holding together and retaining its shape	a businessman who buys or sells for another in exchange for a commission
the idea that is intended	a representative who acts on behalf of other persons or organizations
the choicest or most essential or most vital part of some idea or experience	any agent or representative of a federal agency or bureau
content communicating a message; what something is about	a substance that exerts some force or effect
considerable capital (wealth or income)
material of a particular kind or constitution