Payment (whether or not in the form of a cheque) is en route or will be sent shortly. Often used as an excuse to avoid the pressure of creditors or someone expecting payment for goods or services. Primarily heard in UK, Canada. A: "Mr. Smith, your mortgage payment is now two months overdue." B: "The cheque's in the mail, I promise you!" A: "Can you lend me $40 until I get paid next week?" B: "Sure thing, the cheque's in the mail."