Smooth ridges going west (5)
I believe the answer is:
sleek
'smooth' is the definition.
(sleek means smooth or glossy)
'ridges going west' is the wordplay.
'ridges' becomes 'keels' (keel can mean a ridge on a bird's breastbone).
'going west' says the letters should be written in reverse (letters heading to the west or left).
'keels' backwards is 'SLEEK'.
(Other definitions for sleek that I've seen before include "(Of hair) smooth, glossy" , "Velvety" , "Smooth - well-fed" , "with glossy coats" , "Looking prosperous" .)