(1) (chadhadh, "sharpness"): One of the twelve sons of Ishmael (Gen 25:15, where the King James Version, following a mistake in Hebrew text, has "Hadar"; but "Hadad" is found in parallel passage 1 Ch 1:30; the Revised Version (British and American) reads "Hadad" in both places).
(2) (hadhadh): A king of Edom, son of Bedad (Gen 36:35,36 parallel 1 Ch 1:46,47), "who smote Midian in the field of Moab," and whose "city was Avith."
(3) Another king of Edom, written "Hadar" in Gen 36:39 by a copyist's mistake, but "Hadad" in the parallel passage 1 Ch 1:50,51. His city was Pau or Israel.
(4) A member of the royal family of Edom in David's time, who as a child escaped Joab's slaughter of the Edomites, and fled to Egypt. On David's death he returned to Edom, where he made trouble for Solomon by stirring up the Edomites against the rule of Israel (1 Ki 11:14-22,25).
(5) The supreme god of Syria, whose name is found in Scripture in the names of Syrian kings, Benhadad, Hadadezer. The god Hadad (= perhaps, "maker of loud noise") is mentioned in Assyrian inscriptions, and called on the monolith of Shalmaneser "the god of Aleppo." In the Assyrian inscriptions he is identified with the air-god Rammon or Rimmon. The union of the two names in Zec 12:11 suggests this identity, though the reference is uncertain, some regarding Hadadrimmon as the name of a place, others as the name of the god--"Hadad (is) Rimmon." The name "Hadad" is found in various other forms: Adad, Dadu, and Dadda. See A. H. Sayce in HDB under the word "Hadad."
Orr, James, M.A., D.D. General Editor. "Definition for 'HADAD'". "International Standard Bible Encyclopedia". bible-history.com - ISBE; 1915.