a. [ Compar. Mustier superl. Mustiest. ] [ From L. mustum must; or perh. fr. E. moist. Cf. Must, n., Moist. ] 1. Having the rank, pungent, offensive odor and taste which substances of organic origin acquire during warm, moist weather; foul or sour and fetid; moldy; as, musty corn; musty books. Harvey. [ 1913 Webster ]
2. Spoiled by age; rank; stale. [ 1913 Webster ]
The proverb is somewhat musty. Shak. [ 1913 Webster ]
3. Dull; heavy; spiritless. “That he may not grow musty and unfit for conversation.” Addison. [ 1913 Webster ]