n. Naut. 1 (in a square-rigged vessel) the lowest sail on the mainmast. 2 (in a fore-and-aft rigged vessel) a sail set on the after part of the mainmast.
MAINSAIL
Meaning of MAINSAIL in English
Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012