Source : Webster's Revised Unabridged Dictionary (1913)

Proscenium \Pro*sce"ni*um\, n.; pl. {Proscenia}. [L., fr. Gr. ?;
   ? before + ? a tent, a wooden stage, the stage. See {Scene}.]
   1. (Anc. Theater) The part where the actors performed; the
      stage.

   2. (Modern Theater) The part of the stage in front of the
      curtain; sometimes, the curtain and its framework.

Source : WordNet®

proscenium
     n 1: the part of a modern theater stage between the curtain and
          the orchestra (i.e., in front of the curtain) [syn: {apron},
           {forestage}]
     2: the wall that separates the stage from the auditorium in a
        modern theater [syn: {proscenium wall}]
     [also: {proscenia} (pl)]