sea bird vs seabird

sea bird and seabird both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea bird	Yes	No	No	No
seabird	Yes	No	No	No

As nouns, sea bird and seabird are synonyms defined as:

sea bird and seabird: a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.

Other synonyms of sea bird include seafowl.

sea bird (noun)	seabird (noun)
a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.	a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.