pearl diver vs diver

pearl diver and diver both are nouns.

Word	Noun	Adjective	Verb	Adverb
pearl diver	Yes	No	No	No
diver	Yes	No	No	No

As nouns, diver is a hypernym of pearl diver; that is, diver is a word with a broader meaning than pearl diver:

Other hypernyms of pearl diver include frogman, underwater diver.

pearl diver (noun)	diver (noun)
a diver who searches for molluscs containing pearls	large somewhat primitive fish-eating diving bird of the Northern Hemisphere having webbed feet placed far back; related to the grebes
	someone who dives (into water)
	someone who works underwater