caisson vs cofferdam

caisson and cofferdam both are nouns.

Word	Noun	Adjective	Verb	Adverb
caisson	Yes	No	No	No
cofferdam	Yes	No	No	No

As nouns, caisson and cofferdam are synonyms defined as:

caisson and cofferdam: large watertight chamber used for construction under water

Other synonyms of caisson include pneumatic caisson.

caisson (noun)	cofferdam (noun)
large watertight chamber used for construction under water	large watertight chamber used for construction under water
an ornamental sunken panel in a ceiling or dome
a chest to hold ammunition
a two-wheeled military vehicle carrying artillery ammunition