NAHASH (nā'hăsh, Heb. nāhāsh, probably from a root meaning serpent rather than from one meaning oracle or one meaning copper)
An Ammonite king whose harsh demands on the men of Jabesh Gilead led Saul to rally the Israelites against him and to defeat him. This victory proved decisive in making Saul king (1Sam.11.1-1Sam.11.2; 1Sam.12.12).An Ammonite king whose son Hanun David befriended. Mistaking David’s intentions, Hanun insulted David’s messengers. David avenged the insult and had no more trouble with the Ammonites (2Sam.10.1-2Sam.10.19; 1Chr.19.1-1Chr.19.19). His son Shobi brought provisions to David during his flight from Absalom (2Sam.17.27-2Sam.17.29). This Nahash may be the same as no. 1, though the length of time between the beginning of Saul’s reign and the rebellion of Absalom in David’s reign favors the view that no. 2 was a descendant of no. 1.A parent of Abigail and Zeruiah (2Sam.17.25). The state of the Hebrew text is unclear about whether this Nahash was a man or a woman. 1Chr.2.16 calls Jesse father of Abigail and Zeruiah. Either Nahash was their mother, or Nahash was an alternative name for Jesse, or Nahash was the former husband of Jesse’s wife. Nahash is a masculine name.
2. 2 Samuel 17:25 refers to “Abigail the daughter of Nahash, sister of Zeruiah.” Both women are called sisters of David. Perhaps the best explanation is that Nahash was the first husband of David’s mother, the father of the daughters: Abigail, the mother of Amasa, and Zeruiah, mother of Joab, and that these women were the half-sisters of David, the stepdaughters of Jesse (1 Chron 19:1, 2).
International Standard Bible Encyclopedia (1915)
(nachash, "serpent"; Naas):
(1) The father of Abigail and Zeruiah, the sisters of David (2Sa 17:25; compare 1Ch 2:16). The text in 2 S, where this reference is made, is hopelessly corrupt; for that reason there are various explanations. The rabbis maintain that Nahash is another name for Jesse, David’s father. Others think that Nahash was the name of Jesse’s wife; but it is not probable that Nahash could have been the name of a woman. Others explain the passage by making Nahash the first husband of Jesse’s wife, so that Abigail and Zeruiah were half-sisters to King David.
(2) A king of Ammon, who, at the very beginning of Saul’s reign, attacked Jabesh-gilead so successfully, that the inhabitants sued for peace at almost any cost, for they were willing to pay tribute and serve the Ammonites (1Sa 11:1 ). The harsh king, not satisfied with tribute and slavery, demanded in addition that the right eye of every man should be put out, as "a reproach upon Israel." They were given seven days to comply with these cruel terms. Before the expiration of this time, Saul, the newly anointed king, appeared on the scene with an army which utterly routed the Ammonites (1Sa 11:1 ), and, according to Josephus, killed King Nahash (Ant., VI, v, 3).
If the Nahash of 2Sa 10:2 be the same as the king mentioned in 1Sa 11, this statement of Josephus cannot be true, for he lived till the early part of David’s reign, 40 or more years later. It is, of course, possible that Nahash, the father of Hanun, was a son or grandson of the king defeated at Jabesh-gilead by Saul. There is but little agreement among commentators in regard to this matter. Some writers go so far as to claim that "all passages in which this name (Nahash) is found refer to the same individual."
(3) A resident of Rabbath-ammon, the capital of Ammon (2Sa 17:27). Perhaps the same as Nahash (2), which see. His son Shobi, with other trans-Jordanic chieftains, welcomed David at Mahanaim with sympathy and substantial gifts when the old king was fleeing before his rebel son Absalom. Some believe that Shobi was a brother of Hanun, king of Ammon (2Sa 10:1).