trysail

noun

1. A small, strong triangular sail sometimes set in place of the mainsail in heavy weather.

   “I have worked like a Trojan all day, and the idea is realized. Margaret helped me out with suggestions, and Tom Spink did the sailorizing. Over our head, from the jiggermast, the steel stays that carry the three jigger-trysails descend high above the break of the poop and across the main deck to the mizzenmast.”