Small vegetable that's smooth and shiny (5)
I believe the answer is:
sleek
'smooth and shiny' is the definition.
(I've seen this in another clue)
'small vegetable' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'vegetable' becomes 'leek' (leek is a kind of vegetable).
's'+'leek'='SLEEK'
'that's' acts as a link.
(Other definitions for sleek that I've seen before include "Elegant, streamlined" , "Aerodynamic - well-groomed" , "With a smooth, gleaming surface" , "Aerodynamic, streamlined" , "Velvety" .)