Squirm and wither tormentedly (6)

I believe the answer is:

writhe

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'squirm' is the definition.
(synonyms)

'wither tormentedly' is the wordplay.
'wither' can be anagrammed to 'WRITHE'.
Though, I am unsure how this is indicated.

'and' is the link.

Can you help me to learn more?

(Other definitions for writhe that I've seen before include "Struggle" , "Twist in agony" , "worm" , "Twist as in pain" , "It's painful moving" .)

I've seen this clue in the Evening Standard.

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