ammunition chest vs caisson

ammunition chest and caisson both are nouns.

Word	Noun	Adjective	Verb	Adverb
ammunition chest	Yes	No	No	No
caisson	Yes	No	No	No

As nouns, ammunition chest and caisson are synonyms defined as:

ammunition chest (noun)	caisson (noun)
a chest to hold ammunition	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