Answer: machi

AnswerCrossword Clue
MACHI

Yeager's breakthrough

MACHI

Speed of sound

MACHI

Speed at the sound barrier.

MACHI
A certain speed of sound.
MACHI
Speed-of-sound term.
MACHIChuck Yeager's breakthrough
MACHIBarrier-breaking speed
MACHISpeed exceeded by SSTs
MACHIChuck Yeager goal?