Behind those who owe Bill

I believe the answer is:

indebt

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'bill' is the definition.
Both the answer and definition are verbs in their base form.
Perhaps there's an association between them I don't understand?

I cannot understand how the remainder of the clue works.

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(Other definitions for indebt that I've seen before include "Owing something" , "Owing, perhaps money" .)

I've seen this clue in the Irish Times.

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