elephant bird vs ratite bird

elephant bird and ratite bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
elephant bird	Yes	No	No	No
ratite bird	Yes	No	No	No

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

elephant bird: huge (to 9 ft.) extinct flightless bird of Madagascar
ratite bird: flightless birds having flat breastbones lacking a keel for attachment of flight muscles: ostriches, cassowaries, emus, moas, rheas, kiwis, elephant birds

Other hypernyms of elephant bird include flightless bird, ratite.

elephant bird (noun)	ratite bird (noun)
huge (to 9 ft.) extinct flightless bird of Madagascar	flightless birds having flat breastbones lacking a keel for attachment of flight muscles: ostriches, cassowaries, emus, moas, rheas, kiwis, elephant birds