Where does “dau ddeg tair” come from?

dau ddeg tair (Welsh) comes from Welsh tair, from Proto-Celtic tisres, from Proto-Indo-European tisres, from Proto-Indo-European trisres, from Proto-Indo-European tréyes — three.

Ancestry of “dau ddeg tair”, step by step

dau ddeg tair traces back through 3 separate lines of ancestry.

via Welsh tair

StepLanguageWordMeaning
1Welshtairfeminine of tri; three
2Proto-Celtictisres
3Proto-Indo-Europeantisresfeminine nominative/vocative of *tréyes
4Proto-Indo-Europeantrisres
5Proto-Indo-Europeantréyesthree

via Welsh dau

StepLanguageWordMeaning
1Welshdautwo
2Proto-Brythonic*dowtwo
3Proto-Celtic*duwotwo
4Proto-Indo-Europeandwóh₁two

via Welsh deg

StepLanguageWordMeaning
1Welshdegten; Soft mutation of teg
2Proto-Brythonicdegten
3Proto-Celticdekamten
4Proto-Indo-Europeandéḱm̥ten
Every word from Proto-Indo-European tréyes