1. The back of a horse
   "The cowboy spent hours in the saddle on horseback"
    
2. A narrow ridge of hills
   "The road wound its way along the top of the horseback";
   - hogback

1. On the back of a horse
   "he rode horseback to town";
   - ahorse, ahorseback

Derived forms: horsebacks

Type of: body part, ridge, ridgeline

Part of: Equus caballus, horse, hoss [US, informal]

Encyclopedia: Horseback