From WordNet (r) 3.0 (2006) [wn]:
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]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From The Free On-line Dictionary of Computing (8 July 2008) [foldoc]:
Computer Aided Design
CAD
<application> (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)