Wide-mouthed container for Magistrate Queen? (6)

I believe the answer is:

beaker

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'wide-mouthed container' is the definition.
I can't tell whether this definition defines the answer.

'magistrate queen?' is the wordplay.
'magistrate' becomes 'beak' (I've seen this before).
'queen?' becomes 'ER' (abbreviation for Elizabeth Regina).
'beak'+'er'='BEAKER'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for beaker that I've seen before include "Chemistry lab vessel" , "Plastic drinking vessel" , "Plastic cup without a handle" , "Glass container in a laboratory" , "Mug - large glass" .)

I've seen this clue in the Sydney Morning Herald.

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