Bascule

A bascule is a term of engineering. It denotes a counterweight or balance, notably in the case of a bascule bridge. A bascule bridge is one like Tower Bridge in London or North Bridge in Hull in which the roadway (a 'span' or 'leaf') swings up to allow ships to pass. The bascule is the massive structure that pivots in the opposite direction to the spanby counter-balancing its weight.

Etymological note: The word 'bascule' is not formed with the diminutive suffix -cule. It is the French word for 'see-saw', and the verb basculer means 'to rock', 'balance', 'tip' or 'fall over'.