Good to do nothing? Topping (5)
I believe the answer is:
glaze
'topping' is the definition.
(I know that glaze is a type of topping)
'good to do nothing?' is the wordplay.
'good' becomes 'g' (abbreviation).
'to do nothing?' becomes 'laze' (laze around).
'g'+'laze'='GLAZE'
(Other definitions for glaze that I've seen before include "Glassy surface" , "Finish" , "Fit panes of glass to" , "Beggar's Opera Captain" , "very smooth surface" .)