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

• Lexulous
• Wordscraper
• Wordosaur

n. The characteristic of being musty.

n. The quality or state of being musty.

n. The state or quality of being musty or sour; moldiness; damp foulness.

n. the quality of smelling or tasting old or stale or mouldy

"But even if the place had been pitch black, I would have known by its smell—a mix of mustiness, dust, and paint—that I was in an old theater, the kind with worn gilt edges and heavy velvet curtains that hung a little longer each year."

staleness   

wearisomeness    tastelessness    mildew    gunsmoke    understandingextracted