Source : Webster's Revised Unabridged Dictionary (1913)

Rainbow \Rain"bow`\, n. [AS. regenboga, akin to G. regenbogen.
   See {Rain}, and {Bow} anything bent,]
   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.

   Note: 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.

   {Lunar rainbow}, a fainter arch or rainbow, formed by the
      moon.

   {Marine rainbow}, or {Sea bow}, a similar bow seen in the
      spray of waves at sea.

   {Rainbow trout} (Zo["o]l.), a bright-colored trout
      ({Salmoirideus}), native of the mountains of California,
      but now extensively introduced into the Eastern States.
      Japan, and other countries; -- called also {brook trout},
      {mountain trout}, and {golden trout}.

   {Rainbow wrasse}. (Zo["o]l.) See under {Wrasse}.

   {Supernumerary rainbow}, a smaller bow, usually of red and
      green colors only, sometimes seen within the primary or
      without the secondary rainbow, and in contact with them.