bascule

plural bascules

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

   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.]

   2009, w:Sherlock Holmes (2009 film), spoken by Sherlock Holmes (Robert Downey Jr.)

   2 more examples

   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.

   1932, Journal of the Association of Chinese & American Engineers, page 10

   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.

   1986, Jeffrey A. Hess, Historic Highway Bridges in Wisconsin, page 87

2. engineeringThe 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

   1997, Official Gazette of the United States Patent and Trademark Office