rainbow Meaning, Definition & Usage

  1. noun an arc of colored light in the sky caused by refraction of the sun's rays by rain
  2. noun an illusory hope
    • chasing rainbows

WordNet

Rain"bow` noun
Etymology
AS. regenboga, akin to G. regenbogen. See Rain, and Bow anything bent,
Definitions
  1. A bow or arch exhibiting, in concentric bands, the several colors of the spectrum, and formed in the part of the hemisphere opposite to the sun by the refraction and reflection of the sun's rays in drops of falling rain. ✍ Besides the ordinary bow, called also primary rainbow, which is formed by two refractions and one reflection, there is also another often seen exterior to it, called the secondary rainbow, concentric with the first, and separated from it by a small interval. It is formed by two refractions and two reflections, is much fainter than the primary bow, and has its colors arranged in the reverse order from those of the latter.

Webster 1913