Thin layer or plate (6)
I believe the answer is:
lamina
I believe this clue is a double definition.
'thin layer' is the first definition.
(I've seen this before)
'plate' is the second definition.
(anatomical term for a plate or layer)
(Other definitions for lamina that I've seen before include "Flat plate" , "Thin plate or layer" , "Thin plate or scale" .)