Order of payment and Postal order

Order of payment noun - A document ordering the payment of money; drawn by one person or bank on another.

Postal order and order of payment are semantically related. In some cases you can replace phrase "Postal order" with "Order of payment", this phrases are similar.

Postal order noun - A written order for the payment of a sum to a named individual; obtainable and payable at a post office.

Order of payment and postal order are semantically related. You can use "Order of payment" instead a noun phrase "Postal order".