The Collaborative International Dictionary of English v.0.48:

Trysail \Try"sail\, n. (Naut.)
   A fore-and-aft sail, bent to a gaff, and hoisted on a lower
   mast or on a small mast, called the trysail mast, close abaft
   a lower mast; -- used chiefly as a storm sail. Called also
   spencer. --Totten.
   [1913 Webster]