agent
agent (āʹjənt) noun
Abbr. agt.
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; instrument.
4. A force or substance that causes a change: a chemical agent.
5. A representative or official of a government or administrative department of a government: an FBI agent.
6. A spy.
[Middle English, from Latin agēns, agent- present participle of agere, to do.]