Unctuous circle at a film centre (3)

I believe the answer is:

oil

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'unctuous circle at a film centre' is the definition.
I can't judge whether this definition defines the answer.

'circle at a film centre' is the wordplay.
'circle' becomes 'O' (O is a circle).
'at' means one lot of letters go next to another.
'centre' says to take the centre.
The central letters of 'film' are 'il'.
'o'+'il'='OIL'

Can you help me to learn more?

(Other definitions for oil that I've seen before include "Thick liquid that doesn't dissolve in water" , "Lubricant or petroleum" , "Liquid fuel" , "Liquid gold" , "Fluid lubricant" .)

I've seen this clue in the Evening Standard.

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