Longman Dictionary of Contemporary English homepage

Date: 1900-2000
Origin: Ernst Mach (1838-1916), Austrian scientist

Mach

 noun
     
Mach [uncountable]
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
Definition from the Longman Dictionary of Contemporary English
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