A financial instrument backed by a deposit at a certain firm such as a bank that can be easily converted into cash. Bloomberg Financial Dictionary
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a document bought at a bank or post office which can be sent through the post and exchanged for money
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money order UK US noun [C] (UK also postal order) MONEY
► a document that can be bought at a post office as a way of sending money through the mail: »
The terms of payment are cash, money order, or cashier's check.
Financial and business terms. 2012.