Source : Webster's Revised Unabridged Dictionary (1913)

Cad \Cad\, n. [Abbrev. fr. cadet.]
   1. A person who stands at the door of an omnibus to open and
      shut it, and to receive fares; an idle hanger-on about
      innyards. [Eng.] --Dickens.

   2. A lowbred, presuming person; a mean, vulgar fellow. [Cant]
      --Thackeray.

Source : WordNet®

cad
     n 1: someone who is morally reprehensible; "you dirty dog" [syn:
          {bounder}, {blackguard}, {dog}, {hound}, {heel}]
     2: software used in art and architecture and engineering and
        manufacturing to assist in precision drawing [syn: {computer-aided
        design}]

Source : Free On-Line Dictionary of Computing

CAD
     
        {Computer Aided Design}