Glazier's paste (5)
I believe the answer is:
putty
'glazier's paste' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for putty that I've seen before include "Window fixer" , "Malleable form of glas holder" , "Whiting and linseed oil paste" , "Window-sealing paste" , "Glazier's paste" .)