Crossword Genius

— 1 is the speed of sound (4)

Ross

I believe the answer is:

mach

(Other definitions for mach that I've seen before include "Ratio of a body's speed to the speed of sound" , "Number referring to speed of sound" , "Ratio used to measure high speeds" , "Ratio of the speed of a moving body to the speed of sound" , "Austrian physicist, gave name to speed no." .)

I've seen this clue in The Times.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.