The term VARNISH SOURCE is composed of two crossword solutions, SUMAC (5 letters) and RESIN (5 letters). SUMAC is a shrub or small tree that is native to many parts of the world, and its leaves and fruits are used to make a variety of products, including a reddish-brown dye and a type of varnish. RESIN is a natural or synthetic substance that is used to make a variety of products, including varnish. Therefore, VARNISH SOURCE can be defined as the combination of SUMAC and RESIN, which are both used to make varnish.