skysail

noun

1. On historical square-rigged ships, the sail above the royal. Normally it is the uppermost sail, but in some cases it is below the moonraker.

   “Never, in the whole voyage, did our crew spring to it in more lively fashion. And lively fashion was needed to save our gear. As it was, they cut away the remnants of the mizzen-lower-topsail with their sheath-knives, and they loosed the main-skysail out of its bolt-ropes.”