Membrane with some transparency still (4)
I believe the answer is:
cyst
'membrane' is the definition.
(I've seen this before)
'with some transparency still' is the wordplay.
'with' says the answer is hidden in the clue.
'CYST' can be found hidden inside 'some transparency still'.
(Other definitions for cyst that I've seen before include "Abnormal sac formed on or in the body" , "Bladder" , "Thin-walled cavity containing liquid" , "Fluid filled sac" , "Blister" .)