Source : Webster's Revised Unabridged Dictionary (1913)

Music drama \Mu"sic dra`ma\
   An opera in which the text and action are not interrupted by
   set arias, duets, etc., the music being determined throughout
   by dramatic appropriateness; musical drama of this character,
   in general. It involves the use of a kind of melodious
   declamation, the development of leitmotif, great orchestral
   elaboration, and a fusion of poetry, music, action, and scene
   into an organic whole. The term is applied esp. to the later
   works of Wagner: ``Tristan und Isolde,'' ``Die
   Meistersinger,'' ``Rheingold,'' ``Walk["u]re,''
   ``Siegfried,'' ``G["o]tterd["a]mmerung,'' and ``Parsifal.''