Smith's Bible Dictionary
Abi'athar. (father of abundance, that is, liberal). High priest and fourth in descent from Eli. (B.C. 1060-1012). Abiathar was the only one of the all the sons of Ahimelech, the high priest, who escaped the slaughter inflicted upon his father's house by Saul, in revenge for his father's house by Saul, in revenge of his having inquired of the Lord for David and given him the shew-bread to eat. 1 Samuel 22:1.
Abiathar having become high priest fled to David, and was thus enabled to inquire of the Lord for him. 1 Samuel 23:9; 1 Samuel 30:7; 2 Samuel 2:1; 2 Samuel 5:19, etc. He adhered to David in his wanderings while pursued by Saul; he was with him while he reigned in Hebron, and afterwards, in Jerusalem. 2 Samuel 2:1-3. He continued faithful to him in Absalom's rebellion. 2 Samuel 15:24; 2 Samuel 15:29; 2 Samuel 15:35-36; 2 Samuel 17:15-17; 2 Samuel 19:11.
When, however, Adonijah set himself up for David's successor on the throne, in opposition to Solomon, Abiathar sided with him, while Zadok was on Solomon's side. For this Abiathar was deprived of the high priesthood. Zadok had joined David at Hebron, 1 Chronicles 12:28, so that there was henceforth who high priests in the reign of David, and till the deposition of Abiathar by Solomon, when Zadok became the sole high priest.
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Smith, William, Dr. Entry for 'Abiathar'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/a/abiathar.html. 1901.