| Adj. | 1. | subsonic - (of speed) less than that of sound in a designated medium; "aircraft flying at subsonic speeds" Antonyms: sonic, transonic - (of speed) having or caused by speed approximately equal to that of sound in air at sea level; "a sonic boom" supersonic - (of speed) greater than the speed of sound in a given medium (especially air); "a supersonic bomber flies so fast that it must release its bombs while the target is still over the horizon" |