The term 'blood-bank measure' refers to a UNIT of measurement used in the medical field. This UNIT is typically used to measure the amount of blood that is donated or stored in a blood bank. The four-letter UNIT of measurement for this term is 'CC, ' which stands for cubic centimeters. A cubic centimeter is a UNIT of volume equal to one milliliter, and is commonly used to measure the volume of a liquid. In the context of a blood bank, it is used to measure the amount of blood that is donated or stored.