diver vs deep-sea diver

diver and deep-sea diver both are nouns.

Word	Noun	Adjective	Verb	Adverb
diver	Yes	No	No	No
deep-sea diver	Yes	No	No	No

As nouns, deep-sea diver is a hyponym of diver; that is, deep-sea diver is a word with a more specific, narrower meaning than diver:

Other hyponyms of diver include pearl diver, pearler, scuba diver.

diver (noun)	deep-sea diver (noun)
large somewhat primitive fish-eating diving bird of the Northern Hemisphere having webbed feet placed far back; related to the grebes	a diver in the deeper parts of the sea
someone who dives (into water)
someone who works underwater