A son of Zeruiah and a brother of Joab.  When David found Saul and his followers asleep, Abishai asked permission to kill the king; but David would not sanction his doing harm to "the Lord's anointed" (1 Sam. xxvi. 5-9; 2 Sam. ii. 18; 1 Chron. ii. 16).  When Abner, fleeing from the battle at Gibeon, was compelled to kill Asahel, Joab and Abishai, his two brothers, pursued the homicide, but without effect (1 Sam. ii. 18-24).  He was one of David's mighty men, having on one occasion slain 300 of the enemy in a fight (xxiii. 18, 19; 1 Chron. xi. 20).  This he seems to have done unaided; but he must have been at the head of an army when he slew of the Edomites, in the Valley of Salt, 18,000 (1 Chron. xviii. 12). (The Sunday School Teacher's Bible Manual, Hunter, 1894)