Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
proscenium is a noun meaning "the part of a modern theater stage between the curtain and the orchestra (i.e., in front of the curtain)". It carries 2 recorded senses.
the part of a modern theater stage between the curtain and the orchestra (i.e., in front of the curtain)
the wall that separates the stage from the auditorium in a modern theater
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for proscenium come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.