Tree secretion
I believe the answer is:
sap
'tree secretion' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sap that I've seen before include "Vigour, energy" , "trench used in siege" , "Moisture in tree or informal dunce" , "Plant juice; undermine" , "Plant liquid or general vitality" .)