Where does “-dôm” come from?

-dôm (Middle Low German) comes from Old Saxon -dōm, from Old Saxon dōm — state, condition, authority, jurisdiction.

Ancestry of “-dôm”, step by step

Step	Language	Word	Meaning
1	Old Saxon	-dōm	(belonging to a) domain or jurisdiction
2	Old Saxon	dōm	state, condition, authority, jurisdiction