Where does “fastus dies” come from?

fastus dies (Latin) comes from Latin fastus, from Latin fas, from Proto-Indo-European bʰeh₂os, from Proto-Indo-European bʰeh₂-, from Proto-Indo-European bʰeh₂-s-ri-.

Ancestry of “fastus dies”, step by step

StepLanguageWordMeaning
1Latinfastusallowed; A day on which courts sat; court...
2Latinfasdictates of religion, divine law (opp. iūs, human law), or an obligation thereunder
3Proto-Indo-Europeanbʰeh₂osutterance, saying
4Proto-Indo-Europeanbʰeh₂-to shine, glow light; to speak, say
5Proto-Indo-Europeanbʰeh₂-s-ri-
Every word from Proto-Indo-European bʰeh₂-s-ri-