sheep dog vs sheepdog

sheep dog and sheepdog both are nouns.

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

As nouns, sheep dog and sheepdog are synonyms defined as:

sheep dog and sheepdog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other synonyms of sheep dog include shepherd dog.

sheep dog (noun)	sheepdog (noun)
any of various usually long-haired breeds of dog reared to herd and guard sheep	any of various usually long-haired breeds of dog reared to herd and guard sheep