English
frostbow
Blend of frost + rainbow.
Proto-Indo-European *prews- ‘to freeze’
…
Proto-Germanic *frustaz
Proto-West Germanic *frost
Old English frost
Middle English frost ‘Cold or freezing weather’
English frost
Proto-Indo-European *bʰewgʰ- ‘to bend’
…
Proto-Germanic *regnabugô
Proto-West Germanic *regnabogō
Old English reġnboga
Middle English reynbowe
English rainbow
Today it means
noun A white arc or circle in the sky during frosty weather, formed by reflection of sunlight from ice crystals floating in the air.
Language periods are conventional ranges, not dates for this word.
Etymograph / frostbow