spaniel vs gun dog

spaniel and gun dog both are nouns.

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

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

spaniel: any of several breeds of small to medium-sized gun dogs with a long silky coat and long frilled ears
gun dog: a dog trained to work with sportsmen when they hunt with guns

Other hypernyms of spaniel include sporting dog.

spaniel (noun)	gun dog (noun)
any of several breeds of small to medium-sized gun dogs with a long silky coat and long frilled ears	a dog trained to work with sportsmen when they hunt with guns