riding horse vs Equus caballus

riding horse and Equus caballus both are nouns.

Word	Noun	Adjective	Verb	Adverb
riding horse	Yes	No	No	No
Equus caballus	Yes	No	No	No

As nouns, Equus caballus is a hypernym of riding horse; that is, Equus caballus is a word with a broader meaning than riding horse:

riding horse: a lightweight horse kept for riding only
Equus caballus: solid-hoofed herbivorous quadruped domesticated since prehistoric times

Other hypernyms of riding horse include horse.

riding horse (noun)	Equus caballus (noun)
a lightweight horse kept for riding only	solid-hoofed herbivorous quadruped domesticated since prehistoric times