mutt vs domestic dog

mutt and domestic dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
mutt	Yes	No	No	No
domestic dog	Yes	No	No	No

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

mutt: an inferior dog or one of mixed breed
domestic dog: a member of the genus Canis (probably descended from the common wolf) that has been domesticated by man since prehistoric times; occurs in many breeds

Other hypernyms of mutt include Canis familiaris, dog.

mutt (noun)	domestic dog (noun)
an inferior dog or one of mixed breed	a member of the genus Canis (probably descended from the common wolf) that has been domesticated by man since prehistoric times; occurs in many breeds