mew vs sea gull

mew and sea gull both are nouns.

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

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

mew: the common gull of Eurasia and northeastern North America
sea gull: mostly white aquatic bird having long pointed wings and short legs

Other hypernyms of mew include gull, seagull.

mew (noun)	sea gull (noun)
the common gull of Eurasia and northeastern North America	mostly white aquatic bird having long pointed wings and short legs
the sound made by a cat (or any sound resembling this)

mew (verb)	sea gull (verb)
cry like a cat
utter a high-pitched cry, as of seagulls