pneumatic caisson vs cofferdam

pneumatic caisson and cofferdam both are nouns.

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

As nouns, pneumatic caisson and cofferdam are synonyms defined as:

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

Other synonyms of pneumatic caisson include caisson.

pneumatic caisson (noun)	cofferdam (noun)
large watertight chamber used for construction under water	large watertight chamber used for construction under water