Source of maple syrup (3)
I believe the answer is:
sap
'source of maple syrup' 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 "dig tunnels" , "Fluid in plant stem" , "Weak foolish person" , "Moisture in tree or informal dunce" , "trench used in siege" .)