1. having the most stale, damp, or moldy smell or taste
Usage: superlative form of musty
2. most outdated or old-fashioned
Usage: figurative use

Examples

• The basement had the mustiest smell in the entire house.
• These are the mustiest books I’ve ever found in an old library.
• The attic was the mustiest room after years of being sealed shut.
• His ideas about technology are the mustiest I’ve heard.
• The mustiest corner of the warehouse hadn’t been cleaned in decades.
• She opened the mustiest trunk filled with old clothes.