mainsail[mān′sāl′; naut., -səl]
- in a square-rigged vessel, the sail set from the main yard
- in a fore-and-aft-rigged vessel, the large sail set from the after side of the mainmast
- The principal sail of a vessel.
- A quadrilateral or triangular sail set from the after part of the mainmast on a fore-and-aft-rigged vessel.
- A square sail set from the main yard on a square-rigged vessel. See Usage Note at boatswain.