caisson

plural caissons

1. engineeringA (permanent) enclosure from which water can be expelled, in order to give access to underwater areas for engineering works etc.

   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

   1 more example

   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

2. engineeringA structure with similar function that is temporary.

   Synonyms: cofferdam, coffer

3. architectureA coffer (sunken panel).
4. The gate across the entrance to a drydock.
5. nauticalA 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. governmentA two-wheeled, horse-drawn military vehicle used to carry ammunition (and a coffin at funerals).

   Near-synonym: limber

   1 more example

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