Where does “seith” come from?

seith (Old Breton) comes from Proto-Brythonic seiθ, from Proto-Celtic sextam, from Proto-Indo-European septḿ̥ — seven.

Ancestry of “seith”, step by step

StepLanguageWordMeaning
1Proto-Brythonicseiθseven
2Proto-Celticsextamseven
3Proto-Indo-Europeanseptḿ̥seven

Words derived from “seith”

Every word from Proto-Indo-European septḿ̥ →Every word from Proto-Celtic sextam →Every word from Proto-Brythonic seiθ →