Arcs of spectrum colors that appear in the sky after rain or when light is refracted through water droplets.
Compound of 'rain' and 'bow' (meaning arc or curved shape), from Old English 'regenboga.' Historically, people saw it as a bow or weapon belonging to rain or the gods.
A rainbow is actually a circle, but we only see an arc from the ground—if you could fly high enough above a rainstorm, you'd see the complete circle, which is why airplane passengers sometimes see rainbow halos.
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