sea gull vs seagull

sea gull and seagull both are nouns.

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

As nouns, sea gull and seagull are synonyms defined as:

sea gull and seagull: mostly white aquatic bird having long pointed wings and short legs

Other synonyms of sea gull include gull.

sea gull (noun)	seagull (noun)
mostly white aquatic bird having long pointed wings and short legs	mostly white aquatic bird having long pointed wings and short legs