kelpie vs sheep dog

kelpie and sheep dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
kelpie	Yes	No	No	No
sheep dog	Yes	No	No	No

As nouns, sheep dog is a hypernym of kelpie; that is, sheep dog is a word with a broader meaning than kelpie:

kelpie: an Australian sheepdog with pointed ears
sheep dog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other hypernyms of kelpie include sheepdog, shepherd dog.

kelpie (noun)	sheep dog (noun)
an Australian sheepdog with pointed ears	any of various usually long-haired breeds of dog reared to herd and guard sheep
(Scottish folklore) water spirit in the form of a horse that likes to drown its riders