1979 as an abbreviation of compact disc as a digital system of information storage. By 1959 as an abbreviation of certificate of deposit "written statement from a bank acknowledging it has received a sum of money from the person named" (1819).

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Definitions of CD from WordNet
cd (n.)
the basic unit of luminous intensity adopted under the Systeme International d'Unites; equal to 1/60 of the luminous intensity per square centimeter of a black body radiating at the temperature of 2,046 degrees Kelvin;
Synonyms: candle / candela / standard candle
cd (n.)
a debt instrument issued by a bank; usually pays interest;
Synonyms: certificate of deposit
cd (n.)
a digitally encoded recording on an optical disk that is smaller than a phonograph record; played back by a laser;
Synonyms: compact disk / compact disc
cd (adj.)
being one hundred more than three hundred;
Synonyms: four hundred / "
Cd (n.)
a soft bluish-white ductile malleable toxic bivalent metallic element; occurs in association with zinc ores;
Synonyms: cadmium / atomic number "