Where does “volbo” come from?

volbo (Esperanto) comes from German wölben, from Middle High German welben.

volbo (Esperanto): vault

Definitions

Step	Language	Word	Meaning
1	German	wölben	to curve, bend; to curve; to bulge out, to arch
2	Middle High German	welben	—

volbo — Etymology, Origin & Word History | Etymology Explorer