Hadadezer - Not (see the margin) Hadarezer. Hadadezer, is the true form, as seen in the names Benhadad, Hadad (1 Kings 15:18, etc.; 1 Kings 11:14, etc.). Hadad was the chief idol, or sun-god, of the Syrians.
To recover his border - literally, to cause his hand to return. The phrase is used sometimes literally, as e. g. Exodus 4:7; 1 Kings 13:4; Proverbs 19:24; and sometimes figuratively, as Isaiah 1:25; Isaiah 14:27; Amos 1:8; Psalms 74:11. The exact force of the metaphor must in each case be decided by the context. If, as is most probable, this verse relates to the circumstances more fully detailed in 2 Samuel 10:15-19, the meaning of the phrase here will be when he (Hadadezer) went to renew his attack (upon Israel), or to recruit his strength against Israel, at the river Euphrates.