Crossword Genius

Grumble millions express (6)

Ross

I believe the answer is:

mutter

'grumble' is the definition.
(synonyms)

'millions express' is the wordplay.
'millions' becomes 'm' (abbreviation).
'express' becomes 'utter' (synonyms).
'm'+'utter'='MUTTER'

(Other definitions for mutter that I've seen before include "Mumble" , "Speak indistinctly or grumble" , "Speak quietly and indistinctly" , "Talk under one's breath" , "carp, > grouse and > beef" .)

I've seen this clue in The Times.
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