blackcap vs sea gull

blackcap and sea gull both are nouns.

Word	Noun	Adjective	Verb	Adverb
blackcap	Yes	No	No	No
sea gull	Yes	No	No	No

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

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

Other hypernyms of blackcap include gull, seagull.

blackcap (noun)	sea gull (noun)
small brownish-grey warbler with a black crown	mostly white aquatic bird having long pointed wings and short legs
chickadee having a dark crown
small black-headed European gull
raspberry native to eastern North America having black thimble-shaped fruit