compact disk: a digitally encoded recording on an optical disk that is smaller than a phonograph record; played back by a laser
optical disk: a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface
pernicious anemia: a chronic progressive anemia of older adults; thought to result from a lack of intrinsic factor (a substance secreted by the stomach that is responsible for the absorption of vitamin B12)