Like a really bad oil lamp? (6)

I believe the answer is:

wicked

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'bad oil lamp?' is the definition.
'wicked' can be an answer for 'bad' (I've seen this before). I'm not certain of the 'oil lamp?' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for wicked that I've seen before include "A candle is" , "Evil; musical" , "Absorbed in enchanting" , "Ungodly; excellent (sl.)" , "Sinful" .)

I've seen this clue in the Evening Standard.

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