underwater diver vs frogman

underwater diver and frogman both are nouns.

Word	Noun	Adjective	Verb	Adverb
underwater diver	Yes	No	No	No
frogman	Yes	No	No	No

As nouns, underwater diver and frogman are synonyms defined as:

Other synonyms of underwater diver include diver.

underwater diver (noun)	frogman (noun)
someone who works underwater	someone who works underwater