Complain repetitively (6)

I believe the answer is:

murmur

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'complain' is the definition.
(murmuring is a kind of complaining)

I don't understand how the rest of the clue works.

(Other definitions for murmur that I've seen before include "Whisper; complain" , "Speak softly or indistinctly" , "Low indistinct sound" , "Little noise" , "Quiet utterance" .)

I've seen this clue in the Evening Standard.

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