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

• Lexulous
• Wordscraper
• Wordosaur

n. someone who attends the theatre, especially one who does so regularly

n. someone who attends the theater

"Thankfully, they fetched a constable, and the constable, being a theatregoer, recognised him and fetched Tom."

looker    watcher    spectator    viewer    witness   

first-nighter    groundling   

theatergoers