seagull vs sea gull

seagull and sea gull both are nouns.

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

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

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

Other synonyms of seagull include gull.

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