The term PREFIX FOR SECOND can be solved by the word NANO, which is a four letter prefix. NANO is derived from the Greek word for 'DWARF' and is used to refer to something that is extremely small. It is commonly used in scientific contexts to refer to objects that are smaller than a micrometer, such as nanobots or nanomaterials. In this context, it is used as a prefix to refer to something that is second in size or importance.