(adversary) is to be explained either as the proper name of a country or person, as a noun in apposition, or as a verb from a root, rub , "to contend plead." All these senses are represented in the Authorized Version and the marginal readings, (Hosea 5:13; 10:6) and the east preferable has been inserted in the text. Jareb is most probably the name of some city of Assyria or another name of the country itself.
Jareb
2 verses
Hosea
Hosea 5:13
When Ephraim saw his sickness, and Judah saw his wound, then went Ephraim to the Assyrian, and sent to king Jareb: yet could he not heal you, nor cure you of your wound.
Hosea 10:6
It shall be also carried unto Assyria for a present to king Jareb: Ephraim shall receive shame, and Israel shall be ashamed of his own counsel.
From Smith's Bible Dictionary
William Smith, 1884