Window sealant (5)
I believe the answer is:
putty
'window sealant' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for putty that I've seen before include "Malleable form of glas holder" , "Whiting and linseed oil paste" , "Window glass sealant" , "Glazier's paste" , "Glass pane securer" .)