St Bernard vs working dog

St Bernard and working dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
St Bernard	Yes	No	No	No
working dog	Yes	No	No	No

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

St Bernard: a Swiss alpine breed of large powerful dog with a thick coat of hair used as a rescue dog
working dog: any of several breeds of usually large powerful dogs bred to work as draft animals and guard and guide dogs

St Bernard (noun)	working dog (noun)
a Swiss alpine breed of large powerful dog with a thick coat of hair used as a rescue dog	any of several breeds of usually large powerful dogs bred to work as draft animals and guard and guide dogs