rainbow (n.)youdaoicibaDictYouDict[rainbow 词源字典]
Old English renboga; see rain (n.) + bow (n.). Common Germanic compound (Old Frisian reinboga, Old Norse regnbogi, Swedish regenbåge, Dutch regenboog, German Regenbogen). Rainbow trout (1876, American English) so called for its resplendent colors. Old English also had scurboga "shower-bow."[rainbow etymology, rainbow origin, 英语词源]