Other forms: rainbows
A rainbow is the arc of colours that appears in the sky when sunlight passes through rain. A rainbow over the valley, chase a rainbow, the colours of the rainbow.
English convention names seven colours — red, orange, yellow, green, blue, indigo, violet — and the traditional mnemonic is Richard Of York Gave Battle In Vain. Seven is a cultural choice rather than a physical fact; the spectrum is continuous. The rainbow flag is a symbol of LGBT communities and is now one of the word's most recognised uses. Note the fixed phrases: over the rainbow, and a pot of gold at the end of the rainbow, meaning a reward that recedes as you approach it.
1nounrainbowThe arc of colours seen when sunlight passes through rain.
“There was a rainbow right across the estuary.”
2adjectivecoloursMade up of many colours.
“A rainbow flag was hanging from the balcony.”
rainbow is an optical effect.
Old English regnboga is simply rain plus bow, in the old sense of anything curved — the same bow as in a bow and arrow and an elbow. Almost every Germanic language names it the same way, which suggests the compound is very old.
Proto-Indo-European
*bʰewgʰ-
Proto-Germanic
*regnabugô — rainbow
Proto-West Germanic
*regnabogō
Old English
reġnboga — rainbow
Middle English
reynbowe
English, today
rainbow
From Middle English reynbowe, raynbowe, from Old English reġnboga (“rainbow”), from Proto-West Germanic regnabogō, from Proto-Germanic regnabugô (“rainbow”), equivalent to rain + bow. Cognate with West Frisian reinbôge (“rainbow”), Dutch regenboog (“rainbow”), German Regenbogen (“rainbow”), Danish regnbue (“rainbow”), Swedish regnbåge (“rainbow”), Icelandic regnbogi (“rainbow”).
Etymology from Wiktionary, CC BY-SA
Practised in Colors, Shapes & Numbers, Weather & Seasons