horseback

nouns

the back of a horse
horseback
is a part of
solid-hoofed herbivorous quadruped domesticated since prehistoric times
Equus caballus, horse
is a type of (narrower)
any part of an organism such as an organ or extremity
body part
a narrow ridge of hills
hogback, horseback

adverbs

on the back of a horse
"he rode horseback to town"; "managed to escape ahorse"; "policeman patrolled the streets ahorseback"
ahorse, ahorseback, horseback