bronco vs mustang

bronco and mustang both are nouns.

Word	Noun	Adjective	Verb	Adverb
bronco	Yes	No	No	No
mustang	Yes	No	No	No

As nouns, mustang is a hypernym of bronco; that is, mustang is a word with a broader meaning than bronco:

bronco: an unbroken or imperfectly broken mustang
mustang: small hardy range horse of the western plains descended from horses brought by the Spanish

bronco (noun)	mustang (noun)
an unbroken or imperfectly broken mustang	small hardy range horse of the western plains descended from horses brought by the Spanish