A double entry for a transaction that offsets one amount against another on both sides of the cashbook is a

The double entry for a transaction that offsets one amount against another on both sides of the cashbook is called a "contra entry". A contra entry is a type of accounting entry where two transactions are recorded simultaneously, but in opposite directions, in order to offset each other. This means that the amount debited in one account is equal to the amount credited in another account, resulting in a net effect of zero on the total balance sheet. For example, if a company pays off a debt using cash from their bank account, a contra entry will be made in the cashbook. The bank account will be credited with the payment amount, while the cash account will be debited with the same amount. This results in a zero net effect on the total balance sheet because the company's assets (cash) have decreased by the same amount that their liabilities (debt) have decreased. In summary, contra entries are used to record transactions that offset each other, resulting in no net effect on the total balance sheet. They are important in maintaining accurate accounting records and ensuring that financial statements are correct.