Our new 'Word Of The Day' article update : onager , n :
The Asiatic wild ass or hemione (Equus hemionus), an animal of the horse family native to Asia; specifically, the Persian onager, Persian wild ass, or Persian zebra (Equus hemionus onager). (military, historical) A military engine acting like a sling which threw stones from a bag or wooden bucket powered by the torsion from a bundle of ropes or sinews operated by machinery; a torsion catapult.