rad /ˈræd/
 弧度單位
 Rad obs. imp. & p. p. of Read, Rede.
 ◄ ►
 rad
      n 1: a unit of absorbed ionizing radiation equal to 100 ergs per
           gram of irradiated material
      2: the unit of plane angle adopted under the Systeme
         International d'Unites; equal to the angle at the center
         of a circle subtended by an arc equal in length to the
         radius (approximately 57.295 degrees) [syn: radian]