Master controlled flow (6)

I believe the answer is:

stream

I'm a little stuck... Click here to teach me more about this clue!

'flow' is the definition.
(I know that flow is a class)

'master controlled' is the wordplay.
'master' anagrams to 'STREAM'.
But, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for stream that I've seen before include "group of schoolchildren" , "Constant flow of liquid" , "Current - file" , "Brook or small river" , "Flow from master" .)

I've seen this clue in The Daily Express and The Mirror.

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