mach

Noun

WORDNET DICTIONARY

mach(n = noun.person) ernst mach - Austrian physicist and philosopher who introduced the Mach number and who founded logical positivism (1838-1916);

is a kind of philosopher, physicist

mach, n. (in full Mach number) the ratio of the speed of a body to the speed of sound in the surrounding medium.

Idiom

Mach one (or two etc.) the speed (or twice the speed) of sound.

Etymology

E. Mach, Austrian physicist d. 1916