Inner coat layer (6)
I believe the answer is:
lining
'inner coat layer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lining that I've seen before include "Backing for curtain, garment etc" , "Extra layer inside another" , "padding" , "Old song: 'Look for the silver . . .'" , "Inside of coat (or outside of cloud?)" .)