Ithra
ITHRA ĭth’ rə (יִתְרָ֣א). The father of Amasa, who led Absalom’s rebel army. He was married to Abigail, David’s sister (1 Chron 2:17). He is called Ithra the Israelite in 2 Samuel 17:25 (KJV, ASV), but Jether the Ishmaelite in 1 Chronicles 2:17.
International Standard Bible Encyclopedia (1915)
The father of Amasa, commanding general in the rebel army of Absalom. It seems that his mother was Abigail, a sister or half-sister of King David (1Ch 2:17). She is called the sister of Zeruiah, Joab’s mother (2Sa 17:25). In this same passage Ithra is called an "Israelite," but in 1Ch 2:17; 1Ki 2:5,32, we read: "Jether the Ishmaelite."