gaviiform seabird vs seafowl

gaviiform seabird and seafowl both are nouns.

Word	Noun	Adjective	Verb	Adverb
gaviiform seabird	Yes	No	No	No
seafowl	Yes	No	No	No

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

gaviiform seabird: seabirds of the order Gaviiformes
seafowl: a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.

Other hypernyms of gaviiform seabird include sea bird, seabird.

gaviiform seabird (noun)	seafowl (noun)
seabirds of the order Gaviiformes	a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.