Old Irish síi

← Proto-Celtic *swīs (inherited)

← Old Church Slavonic вꙑ (cognate)

← Welsh chwi (cognate)

← Proto-Indo-European *wos (inherited)

← Latin vōs (cognate)

→ Welsh chi (cognate)

→ Irish sibh (cognate)

→ Cornish why (cognate)

→ Cornish hwi (cognate)

→ Old Irish sí (mention)