Find he is shaking like the devil (8)

I believe the answer is:

fiendish

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'like the devil' is the definition.
I can't tell whether this definition defines the answer.

'find he is shaking' is the wordplay.
'shaking' indicates anagramming the letters.
'find'+'he'+'is'='findheis'
'findheis' with letters rearranged gives 'FIENDISH'.

Can you help me to learn more?

(Other definitions for fiendish that I've seen before include "like some Sudokus" , "very hard" , "Like Satan or the devil" , "Diabolical" , "Finished (anag) - demonic" .)

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

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