Abarim Publications' online Biblical Hebrew Dictionary
Besides as the name Arad, the word ערד ('rd) does not exists in the Hebrew of the Bible. Jones' Dictionary of Old Testament Proper Names, however, reports that this root occurs in at least three cognate languages:
This Aramaic noun, however, did make it into the Bible. It occurs in Job 39:5 in the form ערוד ('arod).
Amore common Hebrew word for wild ass is the somewhat similar noun עיר ('ayir), which looks quite like the word עיר ('ir), meaning city. See the name Irad.