ˈeɪ.dʒənt ˈfæktə ˈfæktɚ the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause an active and efficient cause; capable of producing a certain effect their research uncovered new disease agents 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