a basic unit of an absorbed dose of radiation, equal to the absorption of 100 ergs of energy per gram of material or 0.01 joule per kilogram of material (0.01 gray or 1.1 roentgen)
radian(s)
radical
radius
radix
See rad in American Heritage Dictionary 4
(răd)
noun
A unit of energy absorbed from ionizing radiation, equal to 100 ergs per gram or 0.01 joules per kilogram of irradiated material. It has been replaced as a standard scientific unit by the gray.