mustang vs broncho

mustang and broncho both are nouns.

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

As nouns, broncho is a hyponym of mustang; that is, broncho is a word with a more specific, narrower meaning than mustang:

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

Other hyponyms of mustang include bronc, bronco.

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