Noun

1. An active and efficient cause; capable of producing a certain effect
2. A representative who acts on behalf of other persons or organizations
3. A substance that exerts some force or effect
4. A businessman who buys or sells for another in exchange for a commission
5. Any agent or representative of a federal agency or bureau
6. The semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause