Larus ridibundus vs sea gull

Larus ridibundus and sea gull both are nouns.

Word	Noun	Adjective	Verb	Adverb
Larus ridibundus	Yes	No	No	No
sea gull	Yes	No	No	No

As nouns, sea gull is a hypernym of Larus ridibundus; that is, sea gull is a word with a broader meaning than Larus ridibundus:

Larus ridibundus: small black-headed European gull
sea gull: mostly white aquatic bird having long pointed wings and short legs

Other hypernyms of Larus ridibundus include gull, seagull.

Larus ridibundus (noun)	sea gull (noun)
small black-headed European gull	mostly white aquatic bird having long pointed wings and short legs