In this, essentially head's torment (8)

I believe the answer is:

nutshell

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'in this essentially' is the definition.
The definition suggests a singular noun which matches the answer.

'head's torment' is the wordplay.
'head's' becomes 'nuts' (informal term for somebody's head).
'torment' becomes 'hell'.
'nuts'+'hell'='NUTSHELL'

Can you help me to learn more?

(Other definitions for nutshell that I've seen before include "Ten hulls (anag)" , "'In a ..., in essence (8)'" , "Brief facts" , "succinct" , "Kernel holder" .)

I've seen this clue in The Guardian.

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