The Collaborative International Dictionary of English v.0.48:

Theatrical \The*at"ric*al\, a. [L. theatricus, Gr. ?.]
   Of or pertaining to a theater, or to the scenic
   representations; resembling the manner of dramatic
   performers; histrionic; hence, artificial; as, theatrical
   performances; theatrical gestures. -- The*at`ri*cal"i*ty,
   n. -- The*at"ric*al*ly, adv.
   [1913 Webster]

         No meretricious aid whatever has been called in -- no
         trick, no illusion of the eye, nothing theatrical. --R.
                                                  Jefferies.
   [1913 Webster]

WordNet (r) 3.0 (2006):

theatrical
    adj 1: of or relating to the theater
    2: suited to or characteristic of the stage or theater; "a
       theatrical pose"; "one of the most theatrical figures in
       public life" [ant: untheatrical]
    n 1: a performance of a play [syn: theatrical performance,
         theatrical, representation, histrionics]

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "theatrical":
   Roscius, Thespian art, actor, actor-proof, actress, affected,
   all-star, amateur theatricals, antagonist, artificial, bad guy,
   ballet, balletic, barnstormer, camp, campy, character,
   character actor, character man, character woman, child actor,
   cinematic, cinematographic, diseur, diseuse, dramatic,
   dramatic art, dramatic form, dramatic irony, dramatic stroke,
   dramatic structure, dramatical, dramaticism, dramatics, dramatism,
   dramatizer, dramaturgic, dramaturgy, emotionalistic, emotive,
   exaggerated, extravagant, fake, false, feeder, film, filmic, foil,
   forced, grandstand, ham, hammy, heavy, histrio, histrion,
   histrionic, histrionics, histrionism, hysteric, ingenue, insincere,
   juvenile, la-di-da, legitimate, maniere, mannered, matinee idol,
   melodramatic, melodramatics, milked, mime, mimer, mimic,
   monodramatic, monologist, movie, mummer, nonrational, operatic,
   ostentatious, overacted, overacting, overdone, overemotional,
   overplayed, overwrought, pantomime, pantomimist, play construction,
   playactor, player, pretentious, protean actor, reciter, repertory,
   scenic, sensational, sensationalism, sensationalistic, showy,
   soubrette, spectacular, stage, stage performer, stage player,
   stagelike, stageworthy, staginess, stagy, starstruck, stellar,
   stooge, straight man, stroller, strolling player, theaterlike,
   theatric, theatricalism, theatricality, theatricals, theatricism,
   theatrics, thespian, thrown away, trouper, underacted, underplayed,
   unnatural, unreasoning, utility man, vaudevillian, villain