Onagers pl. : of Onager

Example:
Rome Total War - Onagers and Sieging?

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 ... Onagers are a little larger than donkeys at about 290 kilograms (640 lb) and 2.1 metres (6.9 ft) (head-body length), and are a little more horse-like. ...