The stub or remaining part of a check, receipt, or ticket that is kept as a record after the main part is torn off and given to someone else.
From counter- + foil (Old French fueille, meaning 'leaf' or 'page'). This bookkeeping term has been in use since at least the 18th century.
Before computers, counterfoils were genius—banks and businesses could tear off your receipt but keep the duplicate stub showing everything that happened, so dishonest tellers had a much harder time cheating.
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