A river between Israel and Moab that rises in the mountains of Gilead and falls into the Dead Sea. It is now called el-Mujeb. The Amorites extended from the Arnon to the Jabbok.
(https://www.kingjamesbibledictionary.com/Dictionary/arnon)
David shares Amalekite spoils with all the places where David and his men had roamed after their raid on Ziklag
David recovered the people and things of Ziklag from the band of Amalekite raiders and additional spoils. When he returned to Ziklag, he sent part of the spoil to his friends, the elders of Judah, saying, "Here is a present for you from the spoil of the enemies of the LORD." It was for those in Bethel, Ramoth of the Negeb, Jattir, Aroer, Siphmoth, Eshtemoa, Racal, the cities of the Jerahmeelites and Kenites, in Hormah, Borashan, Athach, Hebron, for all the places where David and his men had roamed. (1 Samuel 30)
Jeremiah prophesied to tell it beside the Arnon that Moab is laid waste. (Jeremiah 48:20)