retriever vs gun dog

retriever and gun dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
retriever	Yes	No	No	No
gun dog	Yes	No	No	No

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

retriever: a dog with heavy water-resistant coat that can be trained to retrieve game
gun dog: a dog trained to work with sportsmen when they hunt with guns

Other hypernyms of retriever include sporting dog.

retriever (noun)	gun dog (noun)
a dog with heavy water-resistant coat that can be trained to retrieve game	a dog trained to work with sportsmen when they hunt with guns