a·gent 
(ājənt)
(ājənt)n.
1. One that acts or has the power or authority to act.
2. One empowered to act for or represent another: an author's agent; an insurance agent.
3. A means by which something is done or caused; an instrument.
4. A force or substance that causes a change: a chemical agent; an infectious agent.
5. A representative or official of a government or administrative department of a government: an FBI agent.
6. A spy.
7. Linguistics The argument that expresses the means or cause of an action or event described by a phrase or clause. The noun John is the agent in the clause John threw the ball.
v. a·gent·ed, a·gent·ing, a·gents
v.tr.
To act as an agent or representative for: Who will agent your next book?
v.intr.
To act as an agent or representative.
[Middle English, from Latin agēns, agent-, present participle of agere, to do; see ag- in the Appendix of Indo-European roots.]