Master changes current (6)
I believe the answer is:
stream
'current' is the definition.
(I know that current can be written as stream)
'master changes' is the wordplay.
'changes' indicates an anagram.
'master' is an anagram of 'STREAM'.
(Other definitions for stream that I've seen before include "schoolchildren grouped together" , "Flock" , "Moving water" , "River - current" , "Natural body of running water" .)