Where does “unionach” come from?

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

Ancestry of “unionach”, step by step

StepLanguageWordMeaning
1Welshunionexact
2Welshunonly; one; one, individual
3Middle Welshunone
4Proto-Brythonicʉnone
5Proto-Celticoinosone
6Proto-Indo-Europeanóynosone; single
Every word from Proto-Indo-European óynos →Every word from Proto-Celtic oinos →Every word from Proto-Brythonic ʉn →