oceanic bird vs seabird

oceanic bird and seabird both are nouns.

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

As nouns, seabird is a hypernym of oceanic bird; that is, seabird is a word with a broader meaning than oceanic bird:

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

Other hypernyms of oceanic bird include sea bird, seafowl.

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