trysail

A small fore-and-aft sail hoisted abaft the foremast and mainmast in a storm to keep a ship’s bow to the wind.

A fore-and-aft sail set with a gaff and sometimes with a boom on the foremast and mainmast of ships, or on a small mast called a trysail-mast. See mast.

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.

A small, strong 3-sided sail sometimes set in place of the mainsail in heavy weather.