The term 'RAINBOW' can be broken down into two parts: the prefix 'irido' (5 letters) and the root word 'irid' (4 letters). The prefix 'irido' comes from the Greek word 'IRIS', which means 'RAINBOW'. The root word 'irid' is derived from the Latin word 'IRIS', which also means 'RAINBOW'. Together, these two words form the term 'RAINBOW', which is a natural phenomenon that occurs when sunlight is refracted through water droplets in the atmosphere. It is characterized by its vibrant colors, which range from red to violet.