Mrs Grundy's shaky grip (4)

I believe the answer is:

prig

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'mrs grundy's' is the definition.
I can't judge whether this defines the answer.

'shaky grip' is the wordplay.
'shaky' indicates an anagram.
'grip' with letters rearranged gives 'PRIG'.

Can you help me to learn more?

(Other definitions for prig that I've seen before include "Goody-goody" , "Smugly self-righteous person" , "Self-righteous hypocrite" , "Puritan" , "Smug type" .)

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