caisson vs coffer

caisson

noun
  • A coffer. 

  • A chest filled with explosive materials, used like a mine. 

  • A two-wheeled, horse-drawn military vehicle used to carry ammunition (and a coffin at funerals). 

  • A floating tank that can be submerged, attached to an underwater object and then pumped out to lift the object by buoyancy; a camel. 

  • An enclosure from which water can be expelled, in order to give access to underwater areas for engineering works etc. 

  • The gate across the entrance to a dry dock. 

  • A large box to hold ammunition. 

coffer

noun
  • A cofferdam. 

  • An ornamental sunken panel in a ceiling or dome. 

  • A trench dug in the bottom of a dry moat, and extending across it, to enable the besieged to defend it with raking fire. 

  • A strong chest or box used for keeping money or valuables safe. 

  • A supply or store of money, often belonging to an organization. 

verb
  • To put money or valuables in a coffer 

  • To decorate something, especially a ceiling, with coffers. 

How often have the words caisson and coffer occurred in a corpus of books? (source: Google Ngram Viewer )