agent

Concise Oxford English Dictionary © 2008 Oxford University Press:
agent/ˈeɪʤənt/

▶noun

• 1 a person that provides a particular service, typically one organizing transactions between two other parties.

  ■ a person who manages financial or contractual matters for an actor, performer, or writer.

• 2 a person who works in secret to obtain information for a government.

• 3 a person or thing that takes an active role or produces a specified effect.

  ■ Grammar the doer of an action.

• 4 Computing an independently operating program, typically one that performs background tasks such as information retrieval or processing on behalf of a user or other program.

– derivatives
agentive adjective (Grammar).

– origin ME: from L. agent-, agere ‘to do’.