Synthetic resin (5)
I believe the answer is:
epoxy
'synthetic resin' is the definition.
(I know that epoxy is a type of synthetic resin)
This is the entire clue.
(Other definitions for epoxy that I've seen before include "Type of adhesive" , "Hard-setting resin" , "Type of adhesive/paint" , "Adhesive; plastic" , "Type of resin" .)