buster vs horseback rider

buster and horseback rider both are nouns.

Word	Noun	Adjective	Verb	Adverb
buster	Yes	No	No	No
horseback rider	Yes	No	No	No

As nouns, horseback rider is a hypernym of buster; that is, horseback rider is a word with a broader meaning than buster:

Other hypernyms of buster include equestrian.

buster (noun)	horseback rider (noun)
a person (or thing) that breaks up or overpowers something	a person skilled in equitation
a person who breaks horses
a robust child
an informal form of address for a man
a person born in the generation following the baby boom when the birth rate fell dramatically