black-necked stilt vs longlegs

black-necked stilt and longlegs both are nouns.

Word	Noun	Adjective	Verb	Adverb
black-necked stilt	Yes	No	No	No
longlegs	Yes	No	No	No

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

black-necked stilt: stilt of southwestern United States to northern South America having black plumage extending from the head down the back of the neck
longlegs: long-legged three-toed black-and-white wading bird of inland ponds and marshes or brackish lagoons

Other hypernyms of black-necked stilt include Himantopus stilt, long-legs, stilt, stilt plover, stiltbird.

black-necked stilt (noun)	longlegs (noun)
stilt of southwestern United States to northern South America having black plumage extending from the head down the back of the neck	long-legged three-toed black-and-white wading bird of inland ponds and marshes or brackish lagoons