subsonic adjective 4noun 1forms 1 adjective4 •(aviation) less than the speed of sound (in the same medium, and at the same temperature and pressure)But British Airways Flight 112 made the trek in under five hours, setting a new record for the fastest subsonic commercial flight across the Atlantic Ocean. — 2020 •with a Mach number such that 0.3 < Ma < 0.8 (approximately - the exact limits vary between sources) •having a frequency too low to be audible •(literary) very quiet, almost inaudibleThe noise of the ship was all around her. The faint subsonic rumble of the reactor and drive. (Leviathan Wakes, James S. A. Corey) noun1 •an aircraft whose maximum speed is less than the speed of sound formssubsonics
