Where does “seis” come from?

seis (Bikol Central) comes from Spanish seis, from Latin sex, from Proto-Italic seks, from Proto-Indo-European swéḱs — six.

Ancestry of “seis”, step by step

StepLanguageWordMeaning
1Spanishseissix
2Latinsexsix; 6
3Proto-Italicsekssix
4Proto-Indo-Europeanswéḱssix
Every word from Proto-Indo-European swéḱs →Every word from Proto-Italic seks →Every word from Latin sex →