Decoration that's partly cosmetic, in general (5)
I believe the answer is:
icing
'decoration' is the definition.
(icing is a kind of decoration)
'partly cosmetic in general' is the wordplay.
'partly' says the answer is hidden in the clue.
'ICING' is hidden in the letters of 'cosmetic in general'.
'that's' is the link.
(Other definitions for icing that I've seen before include "in the freezer?" , "that finishes off 29 [ANGEL CAKE]" , "Cake frosting" , "it's dangerous on the roads" , "Concreted sugar" .)