D' DISK (5 letters) The term CD PORTION can be broken down into two crossword solutions: CERT (4 letters) and DISK (5 letters). CERT stands for Certificate of Deposit, which is a type of financial instrument that is issued by banks and other financial institutions. It is a form of savings account that pays a fixed rate of interest over a specified period of time. DISK stands for Digital Versatile Disc, which is an optical disc storage medium used to store digital data. It is commonly used for storing audio, video, and computer data.