/hawrs"bak'/ , n.
1. the back of a horse.
2. Geol. a low, natural ridge of sand or gravel; an esker. Cf. hogback .
adv.
3. on horseback: to ride horseback.
adj.
4. made or given in a casual or speculative way; approximate or offhand: a horseback estimate on the construction costs.
[ 1350-1400; ME. See HORSE, BACK 1 ]