Computer-aided design (3)
I believe the answer is:
cad
'computer-aided design' is the definition.
(I know that computer-aided design can be written as CAD)
This is all the clue.
(Other definitions for cad that I've seen before include "Heel" , "One behaves dishonourably" , "A knave, real rotter" , "Dishonourable man of decadent sort" , "That ain't no gentleman" .)