Really wild beast conserving energy in cathedral city (9)

I believe the answer is:

genuinely

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'really' is the definition.
(I know that really can be written as genuinely)

'wild beast conserving energy in cathedral city' is the wordplay.
'wild beast' becomes 'gnu' (I've seen this before. I am not sure about the 'wild' bit.).
'conserving' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mcn).
'cathedral city' becomes 'Ely' (English city with a cathedral).
'gnu' enclosing 'e' is 'genu'.
'genu'+'in'+'ely'='GENUINELY'

Can you help me to learn more?

(Another definition for genuinely that I've seen is " Truly".)

I've seen this clue in The Independent.

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