Definition of "agent"

agent

/ˈeɪ.d͡ʒənt/

noun
plural agents
1. One who exerts power, or has the power to act
  Quotations
  Seeing we are so wonderfully endowed with priceless gifts by our Heavenly Father, will he not require usury at our hands? He will. But he has made us agents to ourselves, which makes us responsible for the way in which we use the talents he has given us, for the manner we expend the gold and silver, the wheat and fine flour, the cattle upon a thousand hills, and the wine and oil, for they all belong to Him
  1862, Brigham Young, “Call for Teams to Go to the Frontiers, etc.”, in Journal of Discourses, volume 9
2. One who acts for, or in the place of, another (the principal), by that person's authority; someone entrusted to do the business of another
  Quotations
  I see in him [Moby Dick] outrageous strength, with an inscrutable malice sinewing it. That inscrutable thing is chiefly what I hate; and be the white whale agent, or be the white whale principal, I will wreak that hate upon him.
  1851 November 14, Herman Melville, chapter 36, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley
3. A person who looks for work for another person
  Quotations
  Ronald Koeman has agreed a deal with Everton to become their new manager, his agent has reportedly told Dutch media. The agent Rob Jansen said, according to the popular Voetbal International website, that it was now down to Southampton and Everton to agree a compensation package for the Dutchman, who has a year remaining on his contract at St Mary’s.
  4 June 2016, Press Association, Ronald Koeman’s agent says Dutchman has agreed terms with Everton
4. Someone who works for an intelligence agency
5. An active power or cause or substance; something (e.g. biological, chemical, thermal, etc.) that has the power to produce an effect
  Quotations
  So far seems to be the work of chemistry alone; at least we have no right to conclude that any other agent interferes; since hay, when it happens to imbibe moisture, exhibits nearly the same processes."
  1807, James Edward Smith, chapter 11, in An introduction to physiological and systematical botany
6. (computing) In the client-server model, the part of the system that performs information preparation and exchange on behalf of a client or server. Especially in the phrase “intelligent agent” it implies some kind of autonomous process which can communicate with other agents to perform some collective task on behalf of one or more humans.
7. (grammar) The participant of a situation that carries out the action in this situation, e.g. "the boy" in the sentences "The boy kicked the ball" and "The ball was kicked by the boy".
  Quotations
  A verb is typically described as active when its subject is the agent or actor. By contrast, a verb is said to be passive when the subject does not perform the action, but is the patient, target, or undergoer of the action.
  2009, Tarsee Li, The Verbal System of the Aramaic of Daniel: An Explanation in the Context of Grammaticalization, page 58
8. (gambling) A cheat who is assisted by dishonest casino staff.
  Quotations
  Nevada casinos are fleeced out of millions of dollars yearly by agents (cheats acting as players) in collusion with crooked Black Jack dealers and pit bosses.
  1978, John Scarne, Scarne's guide to casino gambling, page 108