Master tricky current (6)
I believe the answer is:
stream
'current' is the definition.
('stream' can be a synonym of 'current')
'master tricky' is the wordplay.
'tricky' indicates an anagram.
'master' is an anagram of 'STREAM'.
(Other definitions for stream that I've seen before include "group of schoolchildren" , "Brook or small river" , "Torrent" , "Small watercourse" , "divide pupils into ability groups" .)