[1] : The Collaborative International Dictionary of English v.0.48

mainsheet \main"sheet`\, n. naut.
   one of the ropes by which the mainsail is hauled aft and
   trimmed.
   1913 webster

[2] : WordNet (r) 2.0

mainsheet
     n : nautical a line rope or chain that regulates the angle
         at which a sail is set in relation to the wind syn: sheet,
          tack, weather sheet, shroud
see also:
sheet tack weather sheet shroud 

Mainsheet >> M Words
Mainsheet, definition of term: Mainsheet
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