sheepdog vs sheep dog

sheepdog and sheep dog both are nouns.

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

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

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

Other synonyms of sheepdog include shepherd dog.

sheepdog (noun)	sheep dog (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