Rashi on Numbers 34:7/רש"י על במדבר ל״ד:ז׳

1גבול צפון means THE NORTHERN BOUNDARY.

2מן הים הגדול תתאו לכם הר ההר FROM THE GREAT SEA YE SHALL MARK OUT YOUR LINE UNTO MOUNT HOR, which is at the north-west corner, and its top slopes down and goes to the sea and there is some of the breadth of the sea inward of it and outside it.

3תתאו means, YE MUST MOVE IN A SLANTING DIRECTION so as to move from west to north to Mount Horayot

4תתאו is an expression denoting “a slanting turn”, just as in (1 Kings 14:28) “the slanting chamber (תא) of the runners" and (Ezekiel 40:10) “and the slanting chambers (תאי) of the gate”. The תא is a chamber with a sloping roof, which is called in O. F. apendiz; it is called תא because it leans and slopes (a lean-to or panthouse).