Etymology

Noun

1. A multicoloured arch in the sky, produced by prismatic refraction of light within droplets of rain in the air.
2. Any prismatic refraction of light showing a spectrum of colours.
3. A wide assortment; a varied multitude.

   a rainbow of possibilities

4. An illusion, mirage

   Many electoral promises are rainbows, vanishing soon after poll day.

5. A curveball, particularly a slow one
6. In Texas hold 'em or Omaha hold 'em, a flop that contains three different suits

Adjective

1. having, or shining with, the colors of the rainbow: iridescent
2. multicoloured
3. special, enigmatic
4. having multiple suits of cards