Possible Clues:

• Refracting device
• Glass triangle that separates light into the colour spectrum
• Light-refracting object
• Spectroscope part
• Refracting polyhedron
• Transparent 3-sided object that separates light into colours
• The 'Dark Side of the Moon' cover has one
• Refracting glass
• Spectrum-showing device
• Spectrum-forming crystal