caisson

/ˈkeɪsɑn/
noun
  1. A large watertight chamber used for construction work underwater, such as building bridge foundations.
    • Diving bells are an early type of caisson used for underwater repairs.
    • The engineers lowered a massive caisson into the harbor to create a dry work area.
    • Workers inside the caisson dug deep into the riverbed to build the bridge's support.
  2. A chest or wagon for carrying ammunition, especially in historical military use.
    • The museum displayed a Civil War caisson used to transport artillery shells.
    • A horse-drawn caisson carried ammunition to the front lines.
    • The soldiers loaded the cannonballs into the caisson before the battle.
  3. A decorative sunken panel in a ceiling, often in a coffered design.
    • Each caisson in the cathedral's ceiling was painted with a different scene.
    • The architect added wooden caissons to give the room a classic look.
    • The old library had a beautiful ceiling with carved caissons.
Synonyms
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