mus·ty / ˈməstē/ • adj. (mus·ti·er, mus·ti·est) having a stale, moldy, or damp smell: a dark musty library filled with old books. ∎ having a stale taste: the beer tasted sour, thin, and musty. ∎ fig. lacking originality or interest: when I read it again, the play seemed musty.DERIVATIVES: mus·ti·ly / -təlē/ adv.mus·ti·ness n.