Rubber source (5)
I believe the answer is:
latex
'rubber source' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for latex that I've seen before include "Tree fluid used to make rubber" , "Rubbery juice" , "Milky fluid of rubber tree" , "Milky source of rubber" , "Exalt (anag)" .)