\▐rad\ n [radiation absorbed dose] (1918) (1) A deprecated, but still widely used, unit of energy absorbed by a material, including living matter, from exposure to ionizing radiation. 1 rad = 0.01 gray (Gy) = 0.01 J/kg. The abbreviation for the SI unit of plane angular measure, the radian, the angle intercepting a circular arc of length equal to its radius (= 360o/2π = 57.3°) (Lide DR (ed) (2004) CRC handbook of chemistry and physics. CRC Press, Boca Raton, FL; (2003) College physics. McGraw-Hill Science/Engineering/Math, New York).