ridgeline vs horseback

ridgeline and horseback both are nouns.

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

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

Other hyponyms of ridgeline include arete, hogback.

ridgeline (noun)	horseback (noun)
a long narrow range of hills	the back of a horse
	a narrow ridge of hills

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