Easton's Bible Dictionary (1897)
Brother of insipidity or impiety, a man greatly renowned for his sagacity among the Jews. At the time of Absalom’s revolt he deserted David (Ps. 41:9; 55:12-14) and espoused the cause of Absalom (2 Sam. 15:12). David sent his old friend Hushai back to Absalom, in order that he might counteract the counsel of Ahithophel (2 Sam. 15:31-37).
This end was so far gained that Ahithophel saw he had no longer any influence, and accordingly he at once left the camp of Absalom and returned to Giloh, his native place, where, after arranging his wordly affairs, he hanged himself, and was buried in the sepulchre of his fathers (2 Sam. 17:1-23). He was the type of Judas (Ps. 41:9).
Smith's Bible Dictionary (1863)
(brother of foolishness), a native of Giloh, was a privy councillor of David, whose wisdom was highly esteemed, though his name had an exactly opposite signification. ) He was the grandfather of Bathsheba. Comp. (2 Samuel 11:3) with 2Sam 23:34 Ahithophel joined the conspiracy of Absalom against David, and persuaded him to take possession of the royal harem, (2 Samuel 16:21) and recommended an immediate pursuit of David. His advice was wise; but Hushai advised otherwise.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
AHITH'OPHEL (brother of foolishness), a native of Giloh, and the familiar friend, companion, and counsellor of David. Ps 55:12-14; 2 Sam 15:12 ; 1 Chr 27:33. He was the grandfather of Bath-sheba. Cf. 2 Sam 11:3 with 2 Sam 23:34. His wisdom seemed superhuman. 2 Sam 16:23. Absalom persuaded him to join in the conspiracy against his father, David ; but the cunning measures which Ahithophel proposed for the accomplishment of Absalom's ambitious plans were all defeated by the counsel of Hushai.
Ahithophel, seeing that the probable issue would be the utter ruin of Absalom and his cause, which would almost necessarily involve his own destruction, returned at once to Giloh and hanged himself. 2 Sam 17:23.
Hitchcock's Bible Names (1869)
brother of ruin or folly