An arch of colours visible in the sky, caused by the refraction and dispersion of the sun’s light by rain or other water droplets in the atmosphere. The colours of the rainbow are generally said to be red, orange, yellow, green, blue, indigo, and violet.
Usually a particular kind of leprechauns live at the beginning and end of the rainbow. It’s best to avoid seeking them out because leprechauns found at the beginning and end of rainbows are most of the time condescending assholes that will humiliate you intellectually if you ask them about the gold that some legends have said is supposed to be buried under the rainbow. They’ll laugh you out of dodge for believing in such nonsense.
Also, rainbows are pretty.