Secrets in an oil lamp on a pole (7)

I believe the answer is:

cresset

I'm a little stuck... Click here to teach me more about this clue!

'lamp on a pole' is the definition.
'cresset' can be an answer for 'lamp' (thesaurus). I'm not certain of the 'on a pole' bit.

'secrets in an oil' is the wordplay.
'secrets' anagrams to 'CRESSET'.
Though, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for cresset that I've seen before include "Formerly a light" , "Old torch" , "Old form of illumination" , "burning basket" , "Fuel container" .)

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

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