cob vs great black-backed gull

cob and great black-backed gull both are nouns.

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

As nouns, cob and great black-backed gull are synonyms defined as:

cob and great black-backed gull: white gull having a black back and wings

Other synonyms of cob include black-backed gull, Larus marinus.

cob (noun)	great black-backed gull (noun)
adult male swan	white gull having a black back and wings
stocky short-legged harness horse
white gull having a black back and wings
nut of any of several trees of the genus Corylus