- Informal. radical.
- Slang. fine; wonderful.
- a former unit of absorbed ionizing radiation dose equivalent to an energy absorption per unit mass of 0.01 joule per kilogram of irradiated material. 1 rad is equivalent to 0.01 gray
“x-ray dose unit,” 1918, shortened form of radiation (q.v.). As shortened form of radical (n.), it is attested in political slang from 1820. Teen slang sense of “extraordinary, wonderful” is from late 1970s (see radical (adj.)).
- A unit used to measure energy absorbed by a material from radiation. One rad is equal to 100 ergs per gram of material. Many scientists now measure this energy in grays rather than in rads.