horseback vs horse

horseback and horse both are nouns.

Word	Noun	Adjective	Verb	Adverb
horseback	Yes	No	No	Yes
horse	Yes	No	Yes	No

horseback (noun)	horse (noun)
the back of a horse	solid-hoofed herbivorous quadruped domesticated since prehistoric times
a narrow ridge of hills	a chessman shaped to resemble the head of a horse; can move two squares horizontally and one vertically (or vice versa)
	a framework for holding wood that is being sawed
	a padded gymnastic apparatus on legs
	troops trained to fight on horseback

horseback (verb)	horse (verb)
	provide with a horse or horses

horseback (adverb)	horse (adverb)
on the back of a horse