a small, sturdy, triangular sail rigged fore and aft on a gaff, esp. one used in place of the mainsail in stormy weather
Origin of trysailfrom naut. phrase a try, the position of lying to in a storm
A small fore-and-aft sail hoisted abaft a mast in a storm to keep a vessel's bow to the wind.
Origin of trysailFrom obsolete try a lying to, heaving to