rainbow

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An arc of spectral colors, usually identified as red, orange, yellow, green, blue, indigo, and violet, that appears in the sky opposite the sun as a result of the refractive dispersion of sunlight in drops of rain or mist.
• noun A similar arc or band, as one produced by a prism or by iridescence.
• noun A graded display of colors.
• noun An illusory hope.
• noun A diverse assortment or collection.

from The Century Dictionary.

• noun A bow, or an arc of a circle, consisting of the prismatic colors, formed by the refraction and reflection of rays of light from drops of rain or vapor, appearing in the part of the heavens opposite to the sun.
• noun In heraldry, the representation of a half-ring divided into seven concentric narrow rings and arched upward, each end resting on a clump of clouds.
• noun In ornithology, a humming-bird of tho genus Diphlogena, containing two most brilliantly plumaged species, D. iris of Bolivia, and D. hesperus of Ecuador.
• noun The rainbow-fish.
• To color like a rainbow, or so brightly as to suggest the rainbow; curve over or surround, as with a rainbow.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.
• noun a fainter arch or rainbow, formed by the moon.
• noun a similar bow seen in the spray of waves at sea.
• noun (Zoöl.) a bright-colored trout (Salmo irideus), 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.
• noun (Zoöl.) See under Wrasse.
• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A multicoloured arch in the sky, produced by prismatic refraction of light within droplets of rain in the air.
• noun Any prismatic refraction of light showing a spectrum of colours.
• noun often used with “of” A wide assortment; a varied multitude.
• noun An illusion, mirage
• noun baseball A curveball, particularly a slow one
• noun poker slang In Texas hold 'em or Omaha hold 'em, a flop that contains three different suits
• adjective Multicoloured.
• adjective attributive Made up of several races or ethnicities, or (more broadly) of several cultural or ideological factions.
• adjective attributive LGBT.
• adjective poker Composed entirely of different suits.
• verb transitive To pattern with many colours, like a rainbow.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

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