The Collaborative International Dictionary of English v.0.48:

Melodrama \Mel`o*dra"ma\, n. [F. m['e]lodrame, fr. Gr. me`los
   song + dra^ma drama.]
   Formerly, a kind of drama having a musical accompaniment to
   intensify the effect of certain scenes. Now, a drama
   abounding in romantic sentiment and agonizing situations,
   with a musical accompaniment only in parts which are
   especially thrilling or pathetic. In opera, a passage in
   which the orchestra plays a somewhat descriptive
   accompaniment, while the actor speaks; as, the melodrama in
   the gravedigging scene of Beethoven's "Fidelio".
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Drama \Dra"ma\ (dr[aum]"m[.a] or dr[=a]"m[.a]; 277), n. [L.
   drama, Gr. dra^ma, fr. dra^n to do, act; cf. Lith. daryti.]
   1. A composition, in prose or poetry, accommodated to action,
      and intended to exhibit a picture of human life, or to
      depict a series of grave or humorous actions of more than
      ordinary interest, tending toward some striking result. It
      is commonly designed to be spoken and represented by
      actors on the stage.
      [1913 Webster]

            A divine pastoral drama in the Song of Solomon.
                                                  --Milton.
      [1913 Webster]

   2. A series of real events invested with a dramatic unity and
      interest. "The drama of war." --Thackeray.
      [1913 Webster]

            Westward the course of empire takes its way;
            The four first acts already past,
            A fifth shall close the drama with the day;
            Time's noblest offspring is the last. --Berkeley.
      [1913 Webster]

            The drama and contrivances of God's providence.
                                                  --Sharp.
      [1913 Webster]

   3. Dramatic composition and the literature pertaining to or
      illustrating it; dramatic literature.
      [1913 Webster]

   Note: The principal species of the drama are tragedy and
         comedy; inferior species are tragi-comedy,
         melodrama, operas, burlettas, and farces.
         [1913 Webster]

   The romantic drama, the kind of drama whose aim is to
      present a tale or history in scenes, and whose plays (like
      those of Shakespeare, Marlowe, and others) are stories
      told in dialogue by actors on the stage. --J. A. Symonds.
      Dramatic

WordNet (r) 3.0 (2006):

melodrama
    n 1: an extravagant comedy in which action is more salient than
         characterization

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "melodrama":
   Grand Guignol, Passion play, Tom show, antimasque,
   audience success, ballet, blood and thunder, bomb, broadcast drama,
   burlesque show, charade, cliff hanger, closet drama, comedy drama,
   critical success, daytime serial, demonstrativeness, dialogue,
   documentary drama, drama, dramalogue, dramatic play,
   dramatic series, duodrama, duologue, emotional appeal,
   emotionalism, emotionality, emotionalization, emotionalizing,
   emotiveness, emotivity, epic theater, experimental theater,
   extravaganza, failure, flop, gasser, giveaway, happening,
   histrionics, hit, hit show, human interest, improvisational drama,
   legitimate drama, love interest, making scenes, masque,
   melodramatics, minstrel show, miracle, miracle play, monodrama,
   monologue, morality, morality play, music drama, musical revue,
   mystery, mystery play, nonrationalness, opera, pageant, panel show,
   pantomime, pastoral, pastoral drama, piece, play, playlet,
   problem play, psychodrama, quiz show, radio drama, review, revue,
   sensational play, sensationalism, serial, show, sitcom,
   situation comedy, sketch, skit, soap, soap opera, sociodrama,
   spectacle, stage play, stage show, straight drama, success,
   suspense drama, tableau, tableau vivant, talk show, teleplay,
   television drama, television play, theater of cruelty,
   theatricality, theatrics, total theater, unreasoningness,
   variety show, vaudeville, vaudeville show, vehicle, visceralness,
   word-of-mouth success, work, yellow journalism