Adonijah in the Bible Encyclopedia - ISBE

ad-o-ni'-ja ('adhoniyahu or 'adhoniyah, "my lord is Yahweh"): (1) The son of David and Haggith, the forth of David's sons, born in Hebron after David became king of Judah, principally known for his attempt to become king instead of Solomon (2 Sam 3:4; 1 Ch 3:2; 1 Ki 1 and 2). The record gives no details concerning Chileab, the son of David and Abigail. Leaving him out, Adonijah was the oldest living son of David, after the death of Amnon and Absalom. In treating the record it has been needlessly obscured by neglecting or distorting the time data. It says that the rebellion of Absalom broke out "at an end of forty years" (2 Sam 15:7). The natural meaning is not forty years after the last-mentioned preceding date, but at the close of the fortieth calendar year of the reign of David. Since David reigned 40 1/2 years (2 Sam 5:4,5), the close of his fortieth calendar year was the beginning of has last year. That the date intended was at the beginning of a vernal year is confirmed by the references to the season (2 Sam 17:19,28). Instead of giving this number Josephus says that 4 years had elapsed since the last preceding date, which is very likely correct...