megapode vs gallinaceous bird

megapode and gallinaceous bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
megapode	Yes	No	No	No
gallinaceous bird	Yes	No	No	No

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

megapode: large-footed short-winged birds of Australasia; build mounds of decaying vegetation to incubate eggs
gallinaceous bird: heavy-bodied largely ground-feeding domestic or game birds

Other hypernyms of megapode include gallinacean.

megapode (noun)	gallinaceous bird (noun)
large-footed short-winged birds of Australasia; build mounds of decaying vegetation to incubate eggs	heavy-bodied largely ground-feeding domestic or game birds