Thin tissue layer (8)
I believe the answer is:
membrane
'thin tissue layer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for membrane that I've seen before include "Thin sheet covering organs" , "Thin pliable sheet of material" , "Layer surrounding cells" , "Thin sheet as a barrier" , "Thin pliable sheet of body tissue" .)