Flow — discharge (4)
I believe the answer is:
flux
This clue is a double definition.
'flow' is the first definition.
(flux is a kind of flow)
'discharge' is the second definition.
(I've seen this before)
(Other definitions for flux that I've seen before include "Excessive discharge of liquid" , "State of flow and change" , "constant changing" , "Process of flowing" , "Flow of matter" .)