Smooth top of scaly vegetable (5)
I believe the answer is:
sleek
'smooth' is the definition.
(sleeking is a kind of smoothing)
'top of scaly vegetable' is the wordplay.
'top of' suggests taking the first letters.
'vegetable' becomes 'leek' (leek is a kind of vegetable).
The initial letter of 'scaly' is 's'.
's'+'leek'='SLEEK'
(Other definitions for sleek that I've seen before include "Smooth - well-fed" , "Glossy and well fed" , "Aerodynamic - well-groomed" , "With a smooth, gleaming surface" , "Pleasingly smooth" .)