Definition of rainbow noun from the Oxford Advanced Learner's Dictionary

 

rainbow

 noun
noun
BrE BrE//ˈreɪnbəʊ//
 
; NAmE NAmE//ˈreɪnboʊ//
 
Sky
 
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a curved band of different colours that appears in the sky when the sun shines through rain all the colours of the rainbow See related entries: Sky Word Origin Old English regnboga (see rain, bow2).Extra examples A rainbow of medals decorated his chest. Every year the Dutch bulb fields burst into a rainbow of colours. The ice glittered with all the colours of the rainbow.
See the Oxford Advanced American Dictionary entry: rainbow