Where does “Joost” come from?

Joost (Dutch) comes from Dutch Joos, from Medieval Latin Iodocus, from Breton Iodoc, from Breton iudh, from Proto-Celtic yowdos — judge.

Ancestry of “Joost”, step by step

Step	Language	Word	Meaning
1	Dutch	Joos	—
2	Medieval Latin	Iodocus	—
3	Breton	Iodoc	—
4	Breton	iudh	lord
5	Proto-Celtic	yowdos	judge

Joost — Etymology, Origin & Word History | Etymology Explorer