watchdog vs working dog

watchdog and working dog both are nouns.

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

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

watchdog: 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

watchdog (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
a guardian or defender against theft or illegal practices or waste