GNU Collaborative International Dictionary of English

Found one definition

1.       
   Musty , a. [Compar. Mustier ; superl. Mustiest.] [From L. mustum must; or perh. fr. E. moist. Cf. Must, n., Moist.]
   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
   Spoiled by age; rank; stale.
   1913 Webster
   The proverb is somewhat musty.
   Shak.
   
   1913 Webster
   Dull; heavy; spiritless. “That he may not grow musty and unfit for conversation.”
   Addison.
   
   1913 Webster