The Collaborative International Dictionary of English v.0.48:

Tractate \Tract"ate\, n. [L. tractatus a touching, handling,
   treatise. See Tractable, and Tract a treatise, Treaty.]
   A treatise; a tract; an essay.
   [1913 Webster]

         Agreeing in substance with Augustin's, from whose
         fourteenth Tractate on St. John the words are
         translated.                              --Hare.
   [1913 Webster]