black-backed gull vs gull

black-backed gull and gull both are nouns.

Word	Noun	Adjective	Verb	Adverb
black-backed gull	Yes	No	No	No
gull	Yes	No	Yes	No

As nouns, gull is a hypernym of black-backed gull; that is, gull is a word with a broader meaning than black-backed gull:

Other hypernyms of black-backed gull include sea gull, seagull.

black-backed gull (noun)	gull (noun)
white gull having a black back and wings	mostly white aquatic bird having long pointed wings and short legs
	a person who is gullible and easy to take advantage of

black-backed gull (verb)	gull (verb)
	fool or hoax
	make a fool or dupe of