Where does “rost” come from?

rost (Old Saxon) comes from Proto-Germanic rustaz, from Proto-Indo-European rudʰso-, from Proto-Indo-European h₁rewdʰ- — red.

Ancestry of “rost”, step by step

StepLanguageWordMeaning
1Proto-Germanicrustazrust
2Proto-Indo-Europeanrudʰso-red
3Proto-Indo-Europeanh₁rewdʰ-red
Every word from Proto-Indo-European h₁rewdʰ- →Every word from Proto-Indo-European rudʰso- →Every word from Proto-Germanic rustaz →