The Collaborative International Dictionary of English v.0.48:

Agent \A"gent\, a. [L. agens, agentis, p. pr. of agere to act;
   akin to Gr. ? to lead, Icel. aka to drive, Skr. aj. [root]2.]
   Acting; -- opposed to patient, or sustaining, action.
   [Archaic] "The body agent." --Bacon.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Agent \A"gent\, n.
   1. One who exerts power, or has the power to act; an actor.
      [1913 Webster]

            Heaven made us agents, free to good or ill.
                                                  --Dryden.
      [1913 Webster]

   2. One who acts for, or in the place of, another, by
      authority from him; one intrusted with the business of
      another; a substitute; a deputy; a factor.
      [1913 Webster]

   3. An active power or cause; that which has the power to
      produce an effect, such as a physical, chemical, or
      medicinal agent; as, heat is a powerful agent.
      [1913 Webster]

   4. (Biochem., Med.) a chemical substance having biological
      effects; a drug.
      [PJC]

WordNet (r) 3.0 (2006):

agent
    n 1: an active and efficient cause; capable of producing a
         certain effect; "their research uncovered new disease
         agents"
    2: a representative who acts on behalf of other persons or
       organizations
    3: a substance that exerts some force or effect
    4: a businessman who buys or sells for another in exchange for a
       commission [syn: agent, factor, broker]
    5: any agent or representative of a federal agency or bureau
       [syn: agent, federal agent]
    6: the semantic role of the animate entity that instigates or
       causes the happening denoted by the verb in the clause [syn:
       agentive role, agent]

Moby Thesaurus II by Grady Ward, 1.0:

275 Moby Thesaurus words for "agent":
   Charlie McCarthy, Federal, acid, acidity, acolyte, activator,
   actor, adjutant, administrator, advocate, agency, aid, aide,
   aide-de-camp, aider, alkali, alkalinity, alloisomer, amanuensis,
   amicus curiae, ancilla, anion, antacid, appliance, appointee,
   architect, assignee, assistant, atom, attendant, attorney,
   attorney-at-law, author, auxiliary, baggage agent, barrister,
   barrister-at-law, base, begetter, beginner, best man, biochemical,
   broker, business agent, buyer, candidate, catalyst, cation, cause,
   causer, channel, chemical, chemical element, chromoisomer,
   claim agent, clerk, coadjutant, coadjutor, coadjutress, coadjutrix,
   commercial agent, commission agent, commissionaire, commissioner,
   compound, conductor, connection, consignee, contrivance, copolymer,
   counsel, counselor, counselor-at-law, creator, creature,
   customer agent, delegate, deputy, device, dimer, directeur,
   director, distributor, doer, driver, dummy, dupe, effector,
   element, emissary, energizer, engenderer, engineer, envoy,
   executant, executive, executive officer, executor, executrix,
   fabricator, factor, father, fed, federal agent, force,
   freight agent, friend at court, front, front man, functionary,
   general agent, generator, go-between, governor, handler, handmaid,
   handmaiden, heavy chemicals, help, helper, helpmate, helpmeet,
   high polymer, homopolymer, hydracid, implement, impresario,
   ingredient, inorganic chemical, inspirer, instigator, instrument,
   instrumentality, instrumentation, insurance agent, intendant,
   interagent, interceder, intercessor, intermediary, intermediate,
   intermediate agent, intermediator, intermedium, internuncio,
   intervener, interventionist, interventor, ion, isomer, jobber,
   land agent, law agent, lawyer, legal adviser, legal counselor,
   legal expert, legal practitioner, legalist, legate, lever, liaison,
   licensee, lieutenant, link, literary agent, loan agent,
   macromolecule, maker, manager, manipulator, means, mechanism,
   mediary, mediator, medium, metamer, middleman, midwife, minion,
   minister, ministry, molecule, monomer, mother, mouthpiece, mover,
   negotiant, negotiator, negotiatress, negotiatrix, neutralizer,
   news agent, nominee, nonacid, official, ombudsman, operant,
   operative, operator, organ, organic chemical, originator, oxyacid,
   paranymph, paraprofessional, parent, parliamentary agent,
   passenger agent, pawn, performer, perpetrator, pilot, plaything,
   pleader, polymer, power, practitioner, press agent, prime mover,
   primum mobile, proctor, procurator, producer, proxy, pseudoisomer,
   puppet, purchasing agent, radical, reagent, real estate agent,
   rector, representative, responsible person, runner, sales agent,
   sea lawyer, second, secretary, selectee, self-styled lawyer,
   servant, sideman, sire, slave, solicitor, special agent, spokesman,
   spokesperson, spokeswoman, spook, spy, station agent, steersman,
   steward, stooge, subject, substitute, sulfacid, supercargo,
   supporting actor, supporting instrumentalist, surrogate,
   theatrical agent, ticket agent, tie, tool, toy, travel agent,
   trimer, undercover man, vehicle, walking delegate, wholesaler,
   worker



The Free On-line Dictionary of Computing (30 December 2018):

agent

    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 automatic process
   which can communicate with other agents to perform some
   collective task on behalf of one or more humans.

   (1995-04-09)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

AGENT, international law. One who is employed by a prince to manage his
private affairs, or, those of his subjects in his name, near a foreign,
government. Wolff, Inst. Nat. Sec. 1237.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

AGENT, contracts. One who undertakes to manage some affair to be transacted
for another, by his authority on account of the latter, who is called the
principal, and to render an account of it.
     2. There are various descriptions of agents, to whom different
appellations are given according to the nature of their employments; as
brokers, factors, supercargoes, attorneys, and the like; they are all
included in this general term. The authority is created either by deed, by
simple writing, by parol, or by mere employment, according to the capacity
of the parties, or the nature of the act to be done. It is, therefore,
express or implied. Vide Authority.
     3. It is said to be general or special with reference to its object,
i.e., according as it is confined to a single act or is extended to all acts
connected with a particular employment.
     4. With reference to the manner of its execution, it is either limited
or unlimited, i. e. the agent is bound by precise instructions, (q.v.) or
left to pursue his own discretion. It is the duty of an agent, 1, To perform
what he has undertaken in relation to his agency. 2, To use all necessary
care. 3, To render an account. Pothier, Tr. du Contrat de Mandat, passim;
Paley, Agency, 1 and 2; 1 Livrm. Agency, 2; 1 Suppl. to Ves. Jr. 67, 97,
409; 2 Id.  153, 165, 240; Bac. Abr. Master and Servant, 1; 1 Ves. Jr. R.
317. Vide Smith  on Merc. Law, ch. 3, p. 43,. et seq. and the articles
Agency, Authority, and Principal.
     5. Agents are either joint or several. It is a general rule of the
common law, that when an authority is given to two or more persons to do an
act, and there is no several authority given, all the agents must concur in
doing it, in order to bind the principal. 3 Pick. R. 232; 2 Pick. R. 346; 12
Mass. R. 185; Co. Litt. 49 b, 112 b, 113, and Harg. n. 2; Id. 181 b. 6 Pick.
R. 198  6 John. R. 39; 5 Barn. & Ald. 628.
     6. This rule has been so construed that when the authority is given
jointly and severally to three person, two cannot properly execute it; it
must be done by all or by one only. Co. Litt. 181 b; Com. Dig. Attorney, C
11; but if the authority is so worded that it is apparent, the principal
intended to give power to either of them, an execution by two will be valid.
Co. Litt. 49 b; Dy. R. 62; 5 Barn. & Ald. 628. This rule applies to private
agencies: for, in public agencies an authority executed by a major would be
sufficient. 1 Co. Litt. 181b; Com. Dig. Attorney, C 15; Bac. Ab. Authority,
C; 1 T. R. 592.
     7. The rule in commercial transactions however, is very different; and
generally when there are several agents each possesses the whole power. For
example, on a consignment of goods for sale to two factors, (whether they
are partners or not,) each of them is understood to possess the whole power
over the goods for the purposes of the consignment. 3 Wils. R. 94, 114; Story

on Ag. Sec. 43.
     8.  As to the persons who are capable of becoming agents, it may be
observed, that but few persons are excluded from acting as agents, or from
exercising authority delegated to them by others. It is not, therefore,
requisite that a person be sui juris, or capable of acting in his own right,
in order to be qualified to act for others. Infants, femes covert, persons
attainted or outlawed, aliens and other persons incompetent for many
purposes, may act as agents for others. Co. Litt. 62; Bac. Ab. Authority, B;
Com. Dig. Attorney, C 4; Id. Baron and Feme, P 3; 1 Hill, S. Car. R. 271; 4
Wend. 465; 3 Miss. R. 465; 10 John. R. 114; 3 Watts, 39; 2 S. & R. 197; 1
Pet. R. 170.
     9. But in the case of a married woman, it is to be observed, that she
cannot be an agent for another when her husband expressly dissents,
particularly when he may be rendered liable for her acts. Persons who have
clearly no understanding, as idiots and lunatics cannot be agents for
others. Story on Ag. Sec. 7.
    10. There is another class who, though possessing understanding, are
incapable of acting as agents for others; these are persons whose duties and
characters are incompatible with their obligations to the principal. For
example, a person cannot act as agent in buying for another, goods belonging
to himself. Paley on Ag. by Lloyd, 33 to 38; 2 Ves. Jr. 317. 11. An agent
has rights which he can enforce, and is, liable to obligations which he must
perform. These will be briefly considered:
    11. The rights to which agents are entitled, arise from obligations due
to them by their principals, or by third persons.
    12 - 1. Their rights against their principals are, 1., to receive a just
compensation for their services, when faithfully performed, in execution of
a lawful agency, unless such services, are entirely gratuitous, or the
agreement between the parties repels such a claim; this compensation,
usually called a commission, is regulated either by particular agreement,
or by the usage of trade, or the presumed intention of the parties. 8 Bing.
65; 1 Caines, 349; 2 Caines, 357.
         2. To be reimbursed all their just advances, expenses and
disbursements made in the course of their agency, on account of, or for the
benefit of their principal; 2 Liverm. on Ag. 11-23; Story on Ag. Sec. 335;
Story on Bailm. Sec. 196; Smith on Mer. Law, 56; 6 East, 392; and also to be
paid interest upon such advances, whenever from the nature of the business,
or the usage of trade, or the particular agreement of the parties, it may be
fairly presumed to have been stipulated for, or due to the agent. 7 Wend.
315; 3 Binn. 295; 3 Caines, 226; 3 Camp. 467; 15 East, 223.
    13. Besides the personal remedies which an agent has to enforce his
claims against his principal for his commissions and, advancements, he has a
lien upon the property of the principal in his hand. See Lien, and Story on
Ag. Sec. 351 to 390.
    14.-2. The rights of agents against third persons arise, either on
contracts made between such third persons and them, or in consequence of
torts committed by the latter. 1. The rights of agents against third persons
on contracts, are, 1st, when the contract is in writing and made expressly
with the agent, and imports to be a contract personally with him, although
he may be known to act as an agent; as, for example, when a promissory note
is given to the agent as such, for the benefit of his principal, and the
promise is to pay the money to the agent, oe nomine. Story on Ag. 393, 394;
8 Mass. 103; see 6 S.& R. 420; 1 Lev. 235; 3 Camp. 320; 5 B.& A. 27. 2d.
When the agent is the only known or ostensible principal, and therefore, is
in contemplation of law, the real contracting party. Story on Ag. Sec. 226,
270, 399. As, if an agent sell goods of his principal in his own name, as if
he were the owner, he is entitled to sue the buyer in his own name; although
his principal may also sue. 12 Wend. 413; 5 M.& S. 833. And on the other
hand, if he so buy, he may enforce the contract by action. 3d. When,  by the
usage of trade, the agent is authorized to act as owner, or as a principal
contracting party, although his character as agent is known, he may enforce
his contract by action. For example, an auctioner, who sells the goods of
another may maintain an action for the price, because he has a possession
coupled with an interest in the goods, and it is a general rule, that
whenever an agent, though known as such, has a  special property in the
subject-matter of the contract, and not a bare custody, or when he has
acquired an interest, or has a lien upon it, he may sue upon the contract. 2
Esp. R. 493; 1 H. Bl. 81, 84; 6 Wheat. 665; 3 Chit. Com. Law, 10; 3 B. & A.
276. But this right to bring an action by agents is subordinate to the
rights of the principal, who may, unless in particular  cases, where the
agent has a lien, or some other vested right, bring a suit himself, and
suspend or extinguish the right of the agent. 7 Taunt. 237, 243; 2 Wash. C.
C. R. 283. 2. Agents are entitled to actions against third persons for torts
committed against them in the course of their agency. 1st. They may maintain
actions, of trespass or trover against third persons for any torts or
injuries affecting their possession of the goods which they hold as agents.
Story on Ag. Sec. 414; 13 East, 135; 9 B. & Cressw. 208; 1 Hen. Bl. 81. 2d.
When an agent has been induced by the fraud of a third person to sell or buy
goods for his principal, and he has sustained loss, he may maintain an
action against such third person for such wrongful act, deceit, or fraud.
Story on Ag. Sec. 415.
    15.-2. Agents are liable for their acts, 1, to their principals; and
2, to third person.
    16.-1. The liabilities of agents to their principals arise from a
violation of their duties and obligations to the principal, by exceeding
their authority, by misconduct, or by any negligence or omission, or act by
which the principal sustains a loss. 3 B. & Adol. 415; 12 Pick. 328. Agents
may become liable for damages and loss under a special contract, contrary to
the general usages of trade. They may also become responsible when charging
a del credere commission. Story on Ag. Sec. 234.
    17.-2. Agents become liable to third persons; 1st, on their contract;
1, when the agent, undertakes to do an act for another, and does not possess
a sufficient authority from the principal, and that is unknown to the other
party, he will be considered as having acted for himself as a principal. 3
B. 9 Adol. 114. 2. When the agent does not disclose his agency, he will be
considered as a principal; 2 Ep. R. 667; 15 East, 62; 12 Ves. 352; 16
Martin's R. 530; and, in the case of agents or factors, acting for merchants
in a foreign country, they will be considered liable whether they disclose
their principal or not, this being the usage of the trade; Paley on Ag. by
Lloyd, 248, 373; 1 B.& P. 368; but this presumption may be rebutted by proof
of a contrary agreement. 3. The agent will be liable when he expressly, or
by implication, incurs a personal responsibility. Story on Ag. Sec. 156-159.
4. When the agent makes a contract as such, and there is no other
responsible as principal, to whom resort can be had; as, if a man sign a
note as "guardian of AB," an infant; in that case neither the infant nor his
property will be liable, and the agent alone will be responsible. 5 Mass.
299; 6 Mass., 58. 2d. Agents become liable to third persons in regard to
torts or wrongs done by them in the course of their agency. A distinction
has been made, in relation to third persons, between acts of misfeasance and
non-feasance: an agent is, liable for the former, under certain
circumstances, but not for the latter; he being responsible for his non-
feasance only to his principal. Story on Ag. Sec. 309, 310. An agent is
liable for misfeasance as to third persons, when, intentionally or
ignorantly, he commits a wrong, although authorized by his principal,
because no one can lawfully authorize another to commit a wrong upon the
rights or property of another. 1 Wils. R. 328; 1 B. & P. 410. 3d. An agent
is liable to  refund money, when payment to him is void ab initio, so that,
the money was never received for the use of his principal, and he is
consequently not accountable to the latter for it, if he has not actually
paid it over at the time he receives notice of the take. 2 Cowp. 565; 10
Mod. 233; M.& S. 344. But unless "caught with the money in his possession,"
the agent is not responsible. 2 Moore, 5; 8 Taunt. 136; 9 Bing. 878; 7 B.&
C. 111; 1 Cowp. 69; 4 Taunt. 198. This last rule is, however, subject to
this qualification, that the money shall have been lawfully received by the
agent; for if, in receiving it, the agent was a wrongdoer, he will not be
exempted from liability by payment to his principal. 1 Campb. 396; 8 Bing.
424; 1 T. R. 62; 2 Campb. 122; 1 Selw. N. P. 90, n.; 12 M. & W. 688; 6 A.&
Ell. N. S. 280; 1 Taunt. 359; 3 Esp. 153.
    See Diplomatic Agent.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

AGENT, practice. An agent is an attorney who transacts the business of
another attorney.
    2. The agent owes to his principal the unremitted exertions of his skill
and ability, and that all his transactions in that character, shall be
distinguished by punctuality, honor and integrity. Lee's Dict. of Practice.