Onager n. : A military engine acting like a sling, which threw stones from a bag or wooden bucket, and was operated by machinery.

Onager n. : A wild ass, especially the koulan.

Example:
Where can I find plans for an authentic Onager or mangonel?

Taxonomy
Onager, Equus, Equus hemionus, Species, IUCN, free encyclopedia, hemionus, horses, Equus hemionus onager, Equus hemionus kulan, genus Equus, Equids, subspecies, Hybrids, horse species, horse family, Onagers, Clutton-Brock.

Defination from the web:
Onager (Equus hemionus) is a large mammal belonging to the genus Equus of the family Equidae (horse family) and native to the deserts of ... African Wild Ass (E. africanus) · Donkey (E. asinus) · Onager (E. hemionus) · Kiang (E. kiang) Subgenus Dolichohippus: Grévy's Zebra ...