Where does “vasal” come from?

vasal (Middle Dutch) comes from Old French vassal, from Medieval Latin vassallus, from Latin vassus, from Gaulish wassos, from Proto-Celtic wāstos, from Proto-Indo-European h₁weh₂- — to leave, abandon, give out.

Ancestry of “vasal”, step by step

Step	Language	Word	Meaning
1	Old French	vassal	vassal
2	Medieval Latin	vassallus	manservant, domestic, retainer
3	Latin	vassus	vassal of vassals; servant
4	Gaulish	wassos	young man, squire
5	Proto-Celtic	wāstos	empty
6	Proto-Indo-European	h₁weh₂-	to leave, abandon, give out

Every word from Proto-Indo-European h₁weh₂- →Every word from Proto-Celtic wāstos →Every word from Gaulish wassos →