Basque sei

← Spanish seis (cognate)

← Proto-Basque *sei (inherited)

← French six (cognate)

← Latin sex (cognate)

← Portuguese seis (cognate)

← Iberian śei (cognate)

→ Basque hamasei (mention)

→ Basque hogeita sei (mention)

→ Basque berrogeita sei (mention)

→ Basque hirurogeita sei (mention)

→ Basque seigarren (affix)