echelon
n
1 level of authority or responsibility; rank in an organization 职权的等级; 级别
the upper echelons of the Civil Service 政府部门的高层.
2 step-like formation of troops, aircraft, ships, etc 梯形编队
aircraft flying in echelon, ie in a line stretching backwards to the left or right 成梯队飞行的飞机.