mainsail

[ meyn-seyl; Nautical meyn-suh l ]
/ ˈmeɪnˌseɪl; Nautical ˈmeɪn səl /

noun Nautical.

the lowermost sail on a mainmast.

Origin of mainsail

late Middle English word dating back to 1425–75; see origin at main1, sail
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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British Dictionary definitions for mainsail

mainsail
/ (ˈmeɪnˌseɪl, nautical ˈmeɪnsəl) /

noun

nautical the largest and lowermost sail on the mainmast
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012