Bill's idiotic definition of steam? (6)

I believe the answer is:

notice

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'bill's' is the definition.
('notice' can be a synonym of 'bill')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for notice that I've seen before include "'Observe, discern (6)'" , "Take cognisance of, observe" , "Notification" , "'Take heed of, perceive (6)'" , "Observe; advertisement" .)

I've seen this clue in The Guardian.

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