Resin (3)
'resin' is the definition.
(resin secreted by lac insects)
This is the entire clue.
(Other definitions for lac that I've seen before include "Insect-produced resin" , "Ingredient of varnish" , "Stated need" , "Natural product" , "insects secrete this" .)
(Other definitions for sap that I've seen before include "Drain - vital fluid" , "Moisture in wood of a tree" , "Undermine the tree juice" , "One is easily fooled" , "trench used in siege" .)