Keep it closed in order to hum (5)

I believe the answer is:

mouth

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'keep it closed' is the definition.
I can't tell whether this definition defines the answer.

'order to hum' is the wordplay.
'order' is an anagram indicator.
'to'+'hum'='tohum'
'tohum' is an anagram of 'MOUTH'.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for mouth that I've seen before include "River ending" , "River part - conversation opener?" , "Opening; say" , "trap" , "chops" .)

I've seen this clue in the Evening Standard.

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