Type of varnish (7)
I believe the answer is:
lacquer
'type of varnish' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lacquer that I've seen before include "Finish similar to varnish" , "coat for protection" , "Shellac and alcohol hair spray" , "Varnish; hair-spray" , "Hard shiny covering on wood and metal" .)