black-winged stilt vs stiltbird

black-winged stilt and stiltbird both are nouns.

Word	Noun	Adjective	Verb	Adverb
black-winged stilt	Yes	No	No	No
stiltbird	Yes	No	No	No

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

black-winged stilt: stilt of Europe and Africa and Asia having mostly white plumage but with black wings
stiltbird: long-legged three-toed black-and-white wading bird of inland ponds and marshes or brackish lagoons

Other hypernyms of black-winged stilt include Himantopus stilt, long-legs, longlegs, stilt, stilt plover.

black-winged stilt (noun)	stiltbird (noun)
stilt of Europe and Africa and Asia having mostly white plumage but with black wings	long-legged three-toed black-and-white wading bird of inland ponds and marshes or brackish lagoons