Lewis & Short

† ŏnăger and ŏnā̆grus, i, m., = ὄναγρος,

  1. I. a wild ass, Varr. R. R. 2, 6, 3; cf. Col. 6, 37, 3; Plin. 8, 44, 69, § 174: timidi, Verg. G. 3, 409: pulcher, Mart. 13, 100, 1; Vulg. Psa. 103, 11; id. Osee, 8, 9.
  2. II. Transf., a military engine for discharging large stones, Veg. Mil. 4, 22; Amm. 23, 4, 4.