The full spread of visible colour, made by light through water. Also a sign of belonging for those the world tried to exclude.
Old English regnboga, a compound of regn (rain) + boga (bow, arc); the rainbow was named plainly for what it looked like and what made it, long before it carried any meaning beyond weather.
The full spread of visible colour, made by light passing through rain. Its second meaning here — a sign of belonging for those the world tried to exclude — asks nothing of the root but the colours themselves, held together and refusing to be just one.