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