mainsail
/ˈmeɪnseɪl/noun
1- the principal sail of a ship, especially the lowest sail on the mainmast in a square-rigged vessel主帆（尤指有横帆装置船主桅上最低的帆）。
1.1
- the sail set on the after part of the mainmast in a fore-and-aft rigged vessel后帆（指有纵帆装置船上装于主桅后的帆）。