Proto-Celtic *sextam

→ Breton seizh (inherited)

→ Welsh saith (inherited)

→ Irish seacht (inherited)

→ Scottish Gaelic seachd (inherited)

→ Manx shiaght (inherited)

→ Cornish seyth (inherited)

→ Middle Irish secht (inherited)

→ Old Irish secht (inherited)

→ Middle Welsh seith (inherited)