A quadrilateral fore-and-aft sail suspended from a gaff(noun)
WordNet. Princeton University. 2010.
Use "gaffsail" in a sentence
"Her foremast carried an immense lateen sail, her pole mainmast three square sails that could be dropped to the main deck for reefing, and her mizzen a gaffsail, with a square topsail above it."
"Her gaffsail boom was lengthened by a flagstaff, so that on festive occasions (and such it appeared Hadelin considered our departure to be) an overwrought banner could be hung over the water."