n. & adj.
n. 1 an arch of colours (conventionally red, orange, yellow, green, blue, indigo, violet) formed in the sky (or across a cataract etc.) opposite the sun by reflection, twofold refraction, and dispersion of the sun's rays in falling rain or in spray or mist. 2 a similar effect formed by the moon's rays.
adj. many-coloured. rainbow lorikeet a small brightly coloured Polynesian parrot, Trichoglossus haematodus. rainbow trout a large trout, Salmo gairdneri, orig. of the Pacific coast of n. America. secondary rainbow an additional arch with the colours in reverse order formed inside or outside a rainbow by twofold reflection and twofold refraction.
[ OE regnboga (as RAIN, BOW(1)) ]