Wax closure (4)
I believe the answer is:
seal
'wax closure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seal that I've seen before include "Sea mammal in sale" , "Authenticating stamp" , "Mammal; impressed wax" , "Ocean mammal or official stamp." , "Wax stamp" .)