The term 'Computer Central Processing Unit' can be abbreviated to 'MAINFRAME, ' which is a nine-letter word. The mainframe is a type of computer that is used for large-scale computing purposes, such as data processing and transaction processing. It is typically used by large organizations, such as banks and government agencies, due to its ability to process large amounts of data quickly and reliably. Mainframes are also known for their high levels of security, making them ideal for sensitive data.