main-topsail[-sāl′; naut., -səl]
main-topsail definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
the sail set on the main-topmast above the mainsail
main-topsail definition by American Heritage Dictionary
The sail that is set above the mainsail.