Mach mB:k n [U] the speed of esp. an aircraft related to the speed of sound 马赫值（飞行速度与音速之比值） An aircraft travelling at Mach 1 is travelling at the speed of sound--at Mach 2 it is travelling at twice the speed of sound. 马赫值为1的飞机是以音速飞行----马赫值为2是以2倍的音速飞行。