Where does “fordorus” come from?

fordorus (Middle Irish) comes from Middle Irish dorus, from Old Irish dorus, from Proto-Celtic dworestus, from Proto-Celtic *dwār, from Proto-Indo-European dʰwṓr, from Proto-Indo-European dʰwer- — door.

Ancestry of “fordorus”, step by step

StepLanguageWordMeaning
1Middle Irishdorusdoor
2Old Irishdorusdoor
3Proto-Celticdworestusdoor
4Proto-Celtic*dwārdoor
5Proto-Indo-Europeandʰwṓrdoor
6Proto-Indo-Europeandʰwer-door
Every word from Proto-Indo-European dʰwer- →Every word from Proto-Indo-European dʰwṓr →Every word from Proto-Celtic *dwār →