Master adjusts flow (6)
I believe the answer is:
stream
'flow' is the definition.
(I know that stream is a type of flow)
'master adjusts' is the wordplay.
'adjusts' indicates an anagram (I've seen 'adjusting' mean this).
'master' with letters rearranged gives 'STREAM'.
(Other definitions for stream that I've seen before include "Constant flow of liquid" , "Brook or small river" , "Flow from master" , "Small narrow river" , "Rill, brook" .)