Where does “un deg pedair” come from?

un deg pedair (Welsh) comes from Welsh un, from Middle Welsh un, from Proto-Brythonic ʉn, from Proto-Celtic oinos, from Proto-Indo-European óynos — one; single.

Ancestry of “un deg pedair”, step by step

un deg pedair traces back through 3 separate lines of ancestry.

via Welsh un

StepLanguageWordMeaning
1Welshunonly; one; one, individual
2Middle Welshunone
3Proto-Brythonicʉnone
4Proto-Celticoinosone
5Proto-Indo-Europeanóynosone; single

via Welsh pedair

StepLanguageWordMeaning
1Welshpedairfeminine of pedwar; four
2Proto-Celtickʷetesres—
3Proto-Indo-Europeankʷétesresfeminine nominative/vocative of *kʷetwóres
4Proto-Indo-Europeankʷetwóresfour
5Proto-Indo-Europeankʷe-and

via Welsh deg

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