Depression in the smoothness of skin (7)
I believe the answer is:
wrinkle
'depression in the smoothness of skin' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for wrinkle that I've seen before include "clever innovation" , "Depression in the smoothness of a surface, skin perhaps" , "Line (in flesh)" , "Tip; furrow" , "Slight crease in surface" .)