lazy-jack

from The Century Dictionary.

• noun In mech. engin., a jack constructed on the same principle as a lazy-tongs, consisting of compound levers pivoted together.
• noun Nautical, a length of rope rove through a thimble, seized on to the boom-topping lift, and made fast to the boom. When the sail is lowered the jacks prevent the folds of canvas from falling on the deck.