agent

noun

1. 1

   the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause

2. 2

   an active and efficient cause; capable of producing a certain effect

   their research uncovered new disease agents

3. 3

   a businessman who buys or sells for another in exchange for a commission

4. 4

   a representative who acts on behalf of other persons or organizations

5. 5

   any agent or representative of a federal agency or bureau

6. 6

   a substance that exerts some force or effect