"caisson" in the noun sense
1. coffer, caisson, lacunar
an ornamental sunken panel in a ceiling or dome
a two-wheeled military vehicle carrying artillery ammunition
3. caisson, ammunition chest
a chest to hold ammunition
4. caisson, pneumatic caisson, cofferdam
large watertight chamber used for construction under water
Source: WordNet® (An amazing lexical database of English)
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