bascule

Etymology
From.

Noun

 * 1) A counterbalanced structure having one end that rises as the other lowers.
 * 2)  The portion of a breech-loading firearm that pivots open in order to allow access to the chamber.
 * 1)  The portion of a breech-loading firearm that pivots open in order to allow access to the chamber.
 * 1)  The portion of a breech-loading firearm that pivots open in order to allow access to the chamber.
 * 1)  The portion of a breech-loading firearm that pivots open in order to allow access to the chamber.

Etymology
Borrowed from.

Noun

 * 1) balance, balance scales
 * 2) counterweight

Noun

 * 1) seesaw