guard dog vs working dog

guard dog and working dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
guard dog	Yes	No	No	No
working dog	Yes	No	No	No

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

guard dog: a dog trained to guard property
working dog: any of several breeds of usually large powerful dogs bred to work as draft animals and guard and guide dogs

guard dog (noun)	working dog (noun)
a dog trained to guard property	any of several breeds of usually large powerful dogs bred to work as draft animals and guard and guide dogs