white-headed stilt vs stiltbird

white-headed stilt and stiltbird both are nouns.

Word	Noun	Adjective	Verb	Adverb
white-headed stilt	Yes	No	No	No
stiltbird	Yes	No	No	No

As nouns, stiltbird is a hypernym of white-headed stilt; that is, stiltbird is a word with a broader meaning than white-headed stilt:

white-headed stilt: stilt of the southwest Pacific including Australia and New Zealand having mostly white plumage but with black wings and nape of neck
stiltbird: long-legged three-toed black-and-white wading bird of inland ponds and marshes or brackish lagoons

Other hypernyms of white-headed stilt include Himantopus stilt, long-legs, longlegs, stilt, stilt plover.

white-headed stilt (noun)	stiltbird (noun)
stilt of the southwest Pacific including Australia and New Zealand having mostly white plumage but with black wings and nape of neck	long-legged three-toed black-and-white wading bird of inland ponds and marshes or brackish lagoons