This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. Plural form of proscenium.

"A cavernous wonder, here is a cathedral for the self; a magnificent complex of proscenia within which we are both the actors and the crowd, strutting and stopping, walking and watching as we admire ourselves admiring what we've become."

proscenium