the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause | any agent that causes a narrowing of an opening of a blood vessel: cold or stress or nicotine or epinephrine or norepinephrine or angiotensin or vasopressin or certain drugs; maintains or increases blood pressure |
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 | |