/mɑ:k, mæk; mɑk/
n [U] (followed by a number 後接数词) ratio of the speed of sth (esp an aircraft) to the speed of sound 马赫
*an aircraft flying at Mach two, ie twice the speed of sound 以两倍于音速飞行的飞机.

n[U]
[Date: 1900-2000; Origin: Ernst Mach (1838-1916), Austrian scientist]
a unit for measuring speed, especially of an aircraft, in relation to the speed of sound. Mach 1 is the speed of sound, Mach 2 is twice the speed of sound etc
　a plane with a maximum speed of Mach 3