Emily Dickinson Lexicon

CAIS'SON, n. [Fr. from caisse, a chest. See Case.]

1. A wooden chest into which several bombs are put, and sometimes gunpowder, to be laid in the way of an enemy, or under some work of which the enemy intend to possess themselves, and to be fired when they get possession. – Encyc.
2. A wooden frame or chest used in laying the foundation of the pier of a bridge. – Encyc.
3. An ammunition chest or wagon.