cofferdam vs pneumatic caisson

cofferdam and pneumatic caisson both are nouns.

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

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

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

Other synonyms of cofferdam include caisson.

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