rainbow

From Middle English reynbowe, from Old English reġnboga, itself from Proto-West Germanic *regnabogō and Proto-Germanic *regnabugô — a straightforward compound of 'rain' and 'bow,' meaning an arch.

The word has stayed remarkably steady since Old English, always describing the same arched shape appearing after rain.

It shares its roots with West Frisian reinbôge, Dutch regenboog, German Regenbogen, Danish regnbue, Swedish regnbåge, and Icelandic regnbogi — all across Germanic languages, the word is built from the same two pieces: rain and arch.