Horse'back` noun 1. The back of a horse. 2. An extended ridge of sand, gravel, and bowlders, in a half-stratified condition. Agassiz. On horseback , on the back of a horse; mounted or riding on a horse or horses; in the saddle. « The long journey was to ... Found on http://www.encyclo.co.uk/webster/H/63
ahorseadverb on the back of a horse; `he rode horseback to town`; `managed to escape ahorse`; `policeman patrolled the streets ahorseback` Found on https://www.encyclo.co.uk/local/20974