Welsh athro

← Breton aotrou (cognate)

← Proto-Celtic *altrawū (inherited)

← Proto-Celtic *aleti (mention)

← Middle Welsh athro (inherited)

← Middle Welsh athrawon (mention)

→ Breton aotrou (cognate)

→ Welsh athrawes (affix)

→ Welsh prifathro (affix)

→ Welsh prifathrawes (affix)

→ Welsh athrawon (affix)

→ Irish altra (cognate)