caisson

Noun

caisson (plural caissons)

1. A (permanent) enclosure from which water can be expelled, in order to give access to underwater areas for engineering works etc.
   • During the construction of the viaduct, the sinking of the caissons in the river bed caused much difficulty to the engineer and contractors, as a bed of running sand was encountered; in consequence, the expenditure for these foundations proved almost prohibitive.1946 January and February, “Notes and News: Demolition of Rhydyfelin Viaduct”, in Railway Magazine, page 53
   • Caissons were enclosed dry chambers built on river beds to facilitate the construction of bridge piers.2003, Bill Bryson, A Short History of Nearly Everything, BCA, page 213
2. A structure with similar function that is temporary.

   Synonyms:

   cofferdam, coffer

3. A coffer (sunken panel).
4. The gate across the entrance to a drydock.
5. A floating tank that can be submerged, attached to an underwater object and then pumped out to lift the object by buoyancy.
   • Near-synonym: pontoon

   Synonyms:

   camel, sea camel, pontoon

6. A two-wheeled, horse-drawn military vehicle used to carry ammunition (and a coffin at funerals).
   • Near-synonym: limber
   • Over hill, over dale / As we hit the dusty trail, / And those caissons go rolling along.1908, Edmund Louis Gruber, “The Caissons Go Rolling Along”

   Synonyms:

   limber

7. A large box to hold ammunition.
8. A chest filled with explosive materials, used like a mine.