Aerodynamically designed (5)
I believe the answer is:
sleek
'aerodynamically designed' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sleek that I've seen before include "Aerodynamic, streamlined" , "(Of hair) smooth, glossy" , "Smooth - well-fed" , "Looking prosperous" , "with glossy coats" .)