Sap may come from this tree (3)
I believe the answer is:
asp
'tree' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'sap may come from' is the wordplay.
'may come from' indicates anagramming the letters (the answer may come from the same letters).
'sap' with letters rearranged gives 'ASP'.
'this' is the link.
Can you help me to learn more?
(Other definitions for asp that I've seen before include "Small poisonous snake" , "A glider's what's called for" , "Snake, killed Cleopatra" , "It proved deadly for Cleopatra" , "Slithery thing" .)