Where does “Maas” come from?

Maas (Finnish) comes from Dutch Maas, from Middle Dutch Mase, from Old Dutch Masa, from Proto-Germanic Masō, from Proto-Celtic Mosā.

Ancestry of “Maas”, step by step

StepLanguageWordMeaning
1DutchMaasMeuse
2Middle DutchMase—
3Old DutchMasaMeuse
4Proto-GermanicMasōMeuse
5Proto-CelticMosā—
Every word from Proto-Celtic Mosā →Every word from Proto-Germanic Masō →Every word from Old Dutch Masa →