Synonyms for Proscenium (same or very similar meaning)
WordNet sense 1 (the part of a modern theater stage between the curtain and the orchestra (i.e., in front of the curtain)):
apron, forestageWordNet sense 2 (the wall that separates the stage from the auditorium in a modern theater):
proscenium wallFrom the ODE community, based on WordNetadd/edit