Where does “cyfeillion” come from?

cyfeillion (Welsh) comes from Welsh cyfaill, from Proto-Celtic *komaltyos, from Proto-Indo-European h₂él- — to grow, nourish.

Ancestry of “cyfeillion”, step by step

StepLanguageWordMeaning
1Welshcyfaillfriend
2Proto-Celtic*komaltyosfoster-brother
3Proto-Indo-Europeanh₂él-to grow, nourish
Every word from Proto-Indo-European h₂él- →Every word from Proto-Celtic *komaltyos →Every word from Welsh cyfaill →
cyfeillion — Etymology, Origin & Word History | Etymology Explorer