noun
also tri·sail ˈtrīsəl ( usual nautical pronunc ), -ˌsāl
Etymology: try (II) + sail
1. : a fore-and-aft sail bent to a gaff, hoisted on a lower mast or a small mast close abaft and usually connected to a lower mast, and used chiefly as a storm sail — see ship illustration
2. : a small and strongly made sail either triangular or with a very short gaff set in place of the mainsail of a yacht in heavy weather