Source : Webster's Revised Unabridged Dictionary (1913)

Bascule \Bas"cule\, n. [F., a seesaw.]
   In mechanics an apparatus on the principle of the seesaw, in
   which one end rises as the other falls.

   {Bascule bridge}, a counterpoise or balanced drawbridge,
      which is opened by sinking the counterpoise and thus
      lifting the footway into the air.

Source : WordNet®

bascule
     n : a structure in which one end is counterbalanced by the other
         (as in a bascule bridge)