The Collaborative International Dictionary of English v.0.48:
Bareback \Bare"back`\ (b[^a]r"b[a^]k`), adv. On the bare back of a horse, without using a saddle; as, to ride bareback. [1913 Webster]WordNet (r) 3.0 (2006):
bareback adv 1: without a saddle; "she prefers to ride her horse bareback" [syn: bareback, barebacked] adj 1: riding without a saddle; "a bareback rider" [syn: bareback, barebacked]