The term 'Spectrum-Showing Device' can be summarized as a PRISM, which is a five-letter word. A PRISM is a transparent optical element with flat, polished surfaces that refract light. It is used to separate white light into its component colors, creating a spectrum of colors. Prisms are commonly used in scientific experiments to analyze the properties of light and color, as well as in optical instruments such as binoculars and telescopes.