1919, "of or having to do with sound waves beyond the limit of human hearing," from super- + sonic. Attested from 1934 in sense of "exceeding the speed of sound" (especially as a measure of aircraft speed), leaving the original sense to ultrasonic (1923).
supersonic [%PREMIUM_LINK%] (s'pər-sŏn'ĭk) Pronunciation Key
Having a speed greater than that of sound in a designated medium, usually air; having a speed greater than Mach 1. Compare hypersonic, subsonic, transonic.