The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. A lowbred, presuming person; a mean, vulgar fellow. [Cant]
      --Thackeray.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cad
    n 1: someone who is morally reprehensible; "you dirty dog" [syn:
         cad, 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, CAD]

The Free On-line Dictionary of Computing (19 January 2023):

Computer Aided Design
CAD

    (CAD) The part of CAE concerning the drawing
   or physical layout steps of engineering design.  Often found
   in the phrase "CAD/CAM" for ".. manufacturing".

   (1994-11-30)