The term PREFIX FOR 'SECONDS' OR 'PARTICLES' is 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 as a prefix for words related to time, such as nanoseconds, which are one billionth of a second, and particles, such as nanoparticles, which are particles that measure less than 100 nanometers in size.