The Collaborative International Dictionary of English v.0.48:

Cothurn \Co"thurn\ (k?"th?rn), n. [L. cothurnus, Gr. ????. Cf.
   Cothurnus.]
   A buskin anciently used by tragic actors on the stage; hence,
   tragedy in general.
   [1913 Webster]

         The moment had arrived when it was thought that the
         mask and the cothurn might be assumed with effect.
                                                  --Motley.
   [1913 Webster] Cothurnate