Definition of Mach noun from the Oxford Advanced Learner's Dictionary

 

Mach

 noun
noun
BrE BrE//mɑːk//
 
; NAmE NAmE//mɑːk//
 
; BrE BrE//mæk//
 
; NAmE NAmE//mæk//
 
[uncountable]
 
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(often followed by a number) a measurement of speed, used especially for aircraft. Mach 1 is the speed of sound. a fighter plane with a top speed of Mach 3 (= 3 times the speed of sound) Word Origin 1930s: named after E. Mach (1838-1916), Austrian physicist and philosopher of science.
See the Oxford Advanced American Dictionary entry: Mach