subsonic

About 0.36 uses per million words.

Meaning

1. adjective having a frequency too low to be audible
2. adjective very quiet, almost inaudible

   The noise of the ship was all around her. The faint subsonic rumble of the reactor and drive. (Leviathan Wakes, James S. A. Corey)

3. adjective less than the speed of sound (in the same medium, and at the same temperature and pressure)
4. adjective with a Mach number such that 0.3 < Ma < 0.8 (approximately - the exact limits vary between sources)
5. noun an aircraft whose maximum speed is less than the speed of sound

Similar words

infrasonic unacoustic nonsonorous nonaudible unsonorous subdetection nonultrasonic subeffective asonant inaudible

Often followed by

flow and speeds aircraft speed jet to or flows

Word family

subsonically