The Collaborative International Dictionary of English v.0.48:

Actor \Ac"tor\, n. [L. actor, fr. agere to act.]
   1. One who acts, or takes part in any affair; a doer.
      [1913 Webster]

   2. A theatrical performer; a stageplayer.
      [1913 Webster]

            After a well graced actor leaves the stage. --Shak.
      [1913 Webster]

   3. (Law)
      (a) An advocate or proctor in civil courts or causes.
          --Jacobs.
      (b) One who institutes a suit; plaintiff or complainant.
          [1913 Webster]

WordNet (r) 3.0 (2006):

actor
    n 1: a theatrical performer [syn: actor, histrion, player,
         thespian, role player]
    2: a person who acts and gets things done; "he's a principal
       actor in this affair"; "when you want something done get a
       doer"; "he's a miracle worker" [syn: actor, doer,
       worker]

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "actor":
   Artful Dodger, Casanova, Don Juan, Machiavel, Machiavelli,
   Machiavellian, Roscius, actress, affecter, agent, antagonist,
   antihero, architect, author, bad guy, bamboozler, barnstormer,
   befuddler, beguiler, bit, bit part, cast, character,
   character actor, character man, character woman, charmer,
   child actor, counterfeiter, creator, cue, deceiver, deluder,
   diseur, diseuse, dissembler, dissimulator, dodger, doer,
   double-dealer, dramatizer, duper, enchanter, entrancer, executant,
   executor, executrix, fabricator, fake, faker, fat part, feeder,
   foil, fooler, forger, fraud, gay deceiver, heavy, hero, heroine,
   histrio, histrion, hoaxer, hollow man, hypnotizer, impersonator,
   ingenue, jilt, jilter, joker, jokester, juvenile, kidder, lead,
   lead role, leading lady, leading man, leading woman, leg-puller,
   lines, mainstay, maker, man of straw, mannerist, matinee idol,
   medium, mesmerizer, mime, mimer, mimic, misleader, monologist,
   mover, mummer, operant, operative, operator, pantomime,
   pantomimist, paper tiger, part, partaker, participator, party,
   performer, perpetrator, person, personage, phony, piece,
   plagiarist, plagiarizer, playactor, player, practical joker,
   practitioner, pretender, prime mover, producer, protagonist,
   protean actor, ragger, reciter, role, role-player, seducer, sharer,
   side, soubrette, spoofer, stage performer, stage player, stooge,
   straight man, straight part, straw man, stroller, strolling player,
   subject, supporter, supporting character, supporting role,
   sustainer, tease, teaser, theatrical, thespian, title role,
   trouper, upholder, utility man, villain, walk-on, walking part,
   worker



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

Actor

    An object-oriented language for Microsoft
   Windows written by Charles Duff of the Whitewater Group ca.
   1986.  It has Pascal/C-like syntax.  Uses a
   token-threaded interpreter.  Early binding is an option.

   ["Actor Does More than Windows", E.R. Tello, Dr Dobb's J
   13(1):114-125 (Jan 1988)].

   (1994-11-08)


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

actor

   1.  In object-oriented programming, an object
   which exists as a concurrent process.

   2.  In Chorus, the unit of resource
   allocation.

   (1994-11-08)


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

ACTOR, practice. 1. A plaintiff or complainant. 2. He on whom the burden of
proof lies.  In actions of replevin both parties are said to be actors.  The
proctor or advocate in the courts of the civil law, was called actor.