echelon
n
1 level of authority or responsibility; rank in an organization 職權的等級; 級別
the upper echelons of the Civil Service 政府部門的高層.
2 step-like formation of troops, aircraft, ships, etc 梯形編隊
aircraft flying in echelon, ie in a line stretching backwards to the left or right 成梯隊飛行的飛機.