Jebus

trodden hard, or fastness, or "the waterless hill", the name of the Canaanitish city which stood on Mount Zion (Josh 15:8; 18:16; 18:28). It is identified with Jerusalem (q.v.) in (Judg 19:10), and with the castle or city of David (1Chr 11:4; 11:5). It was a place of great natural strength, and its capture was one of David's most brilliant achievements (2Sam 5:8).

EBD - Easton's Bible Dictionary