Liver output (4)
I believe the answer is:
bile
'liver output' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bile that I've seen before include "Gall bladder substance" , "Fluid secreted by the liver" , "Ill-temper" , "Spleen" , "Peevish temper; a liver secretion" .)