bascule

noun

1. A counterbalanced structure having one end that rises as the other lowers.

   “In the late eighties and early nineties several new types of movable spans were advocated, including the pull-back draw, the jackknife span, the bob-tail swing, the horizontal-folding draw, the shearpole draw, the gyratory lift, the transbordeur, the double-cantilever swing, several types of bascule, and the vertical lift.”

   “The study sample contains nine rolling-lift bascules of the type invented by Chicago engineer William Scherzer in 1893 , and refined by the engineering staff of the Scherzer Rolling Lift Bridge Company, also of Chicago.”

   “Look at those towering structures. It’s the first combination of bascule and suspension bridge ever attempted. Most innovative. [In reference to w:Tower Bridge.]”

2. The portion of a breech-loading firearm that pivots open in order to allow access to the chamber.

   “A device for coupling and releasing the trigger mechanism in a bascule of a gun”