what does "in a oner"mean?
“Mr. Strike, your attitude astounds me. You undertook to repay Mr. Rokeby monthly, and you are now in arrears to the tune of—”
“I can’t pay you what I haven’t got. If you hold tight, I should be able to give you all of it back. Maybe even in a oner.”

Question

Answer

"A oner" can refer to a hundred pounds but that doesn't seem quite right here.

Answer

It's not something I have heard before, but my assumption is that it means 'in a one-off payment' - e.g. he will be repaid the entire sum in one payment.

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