Devilish demonstration at central Greenwich (5)

I believe the answer is:

demon

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'devilish demonstration at central greenwich' is the definition.
I can't tell whether this defines the answer.

'demonstration at central greenwich' is the wordplay.
'demonstration' becomes 'demo' (synonyms).
'at' is a charade indicator (letters next to each other).
'central' says to take the centre.
The middle letter of 'greenwich' is 'n'.
'demo'+'n'='DEMON'

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(Other definitions for demon that I've seen before include "Fiend, devil" , "Evil spirit or cruel person" , "Ghoul" , "Genius" , "malignant spirit" .)

I've seen this clue in the Evening Standard.

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