Start to discharge organic substance (6)
I believe the answer is:
tissue
'substance' is the definition.
(I know that tissue is a substance)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tissue that I've seen before include "See 11" , "'Soft, thin paper (6)'" , "Disposable piece of absorbent paper" , "cell block?" , "Paper hankie" .)