Where does “betullus” come from?

betullus (Vulgar Latin) comes from Latin betulla, from Gaulish bitu, from Proto-Celtic betwiyos, from Proto-Indo-European gʷét-.

Ancestry of “betullus”, step by step

Step	Language	Word	Meaning
1	Latin	betulla	—
2	Gaulish	bitu	—
3	Proto-Celtic	betwiyos	—
4	Proto-Indo-European	gʷét-	—

betullus — Etymology, Origin & Word History | Etymology Explorer