Where does “*pʉr” come from?

*pʉr (Proto-Brythonic) comes from Latin pūrus, from Proto-Indo-European pewH- — to be clean, pure.

Ancestry of “*pʉr”, step by step

Step	Language	Word	Meaning
1	Latin	pūrus	—
2	Proto-Indo-European	pewH-	to be clean, pure

*pʉr — Etymology, Origin & Word History | Etymology Explorer