Wither contortedly! (6)

I believe the answer is:

writhe

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'contortedly' is the definition.
I can't judge whether this definition defines the answer.

'wither' is the wordplay.
'wither' anagrams to 'WRITHE'.
But, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for writhe that I've seen before include "Wriggle" , "Thrash" , "Move sinuously" , "feel acute embarrassment" , "Painfully move" .)

I've seen this clue in the Evening Standard.

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