Musty describes a stale, damp smell that comes from things that haven't been exposed to fresh air for a long time. When you open a closet that's been closed all summer, or walk into a basement that nobody uses, that slightly unpleasant, moldy smell is mustiness.

The smell comes from tiny organisms like mold and mildew growing in damp places without good air circulation. Old books sometimes smell musty, especially if they've been stored in humid conditions. Antique stores often have a musty odor from all the old furniture and fabrics.

You might describe a forgotten attic as musty, or say that your grandma's vintage coat has a musty smell until it's been aired out. The word can also describe the actual air in a space: a musty room feels stuffy and stale, like it needs windows thrown open to let in fresh air and sunshine.

Mustiness can be a sign that a space needs better ventilation. Opening windows, using fans, or running a dehumidifier can help clear out mustiness and reduce mold growth.