rainbow

n. Arch of colours formed in the sky by reflection, refraction, and dispersion of the sun's rays in falling rain or in spray or mist. adj. Many-coloured. [old english: related to *rain, *bow1]

n. 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.