hypersonic \hy`per*son"ic\, n. [Pref. hyper- + sonic.]
   (Aeronautics)
   Pertaining to or moving at a speed greatly in excess of the
   speed of sound, usually meaning greater than mach 5. All
   speeds in excess of the speed of sound are supersonic, but
   to be hypersonic requires even higher speed.
   [PJC]