Pneumatic caisson Meaning, Definition & Usage

  1. noun large watertight chamber used for construction under water
    caisson; cofferdam.

WordNet

Definitions
  1. (Engin.), a caisson, closed at the top but open at the bottom, and resting upon the ground under water. The pressure of air forced into the caisson keeps the water out. Men and materials are admitted to the interior through an air lock. See Lock.

Webster 1913