[tran.son.ic] also trans.son.ic adj [trans- + supersonic] (1945) 1: being or relating to speeds near that of sound in air or about 741 miles (1185 kilometers) per hour at sea level and esp. to speeds slightly below the speed of sound at which the speed of airflow varies from subsonic to supersonic at different points along the surface of a body in motion relative to the surrounding air
2: moving, capable of moving, or utilizing air currents moving at a transonic speed