[I]f the czigithai is not the ſame with the zebra, it may be the Aſiatic animal called onager or wild aſs. The onager ſhould not be confounded with the zebra; but I am uncertain whether the ſame remark is applicable to the onager and czigithai; for, from comparing the relations of travellers, it appears, that there are different kinds of wild aſſes, of which the onager is the moſt remarkable. […] The ſwiftneſs of the onager is mentioned by travellers, who remark, that he runs with ſuch rapidity as to eſcape the hunters, though mounted on horſes; […]
Source: wiktionary
The onager, or wild aſs, is ſeen in ſtill greater abundance than the wild horſe; and the peculiarities of its kind are more diſtinctly marked than in thoſe of the tame one.
Source: wiktionary
One of the onagers, however, having hurt its leg, could not be harnessed at present, and a few days' rest was necessary.
Source: wiktionary
The onager, meaning "wild ass," derived its name from its powerful recoil, or kick, upon discharge; […] In addition, although Josephus described an onager in action hurling a 100-pound stone over 400 yards, most onagri achieved a shorter range than the ballista, thus exposing their crews to enemy archers.
Source: wiktionary