rad(n = noun.quantity) radian - 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);
a unit of measurement of the amount of ionizing radiation absorbed by an object, equal to an energy of 100 ergs per gram of irradiated material (equal to 0.01 gray). [PJC]
rad, imp. & p. p.
imp. & p. p. of Read, Rede. Spenser. [1913 Webster]