köken: Etymology tree Esperanto ok Proto-Indo-European *déḱm̥ Proto-Hellenic *dékə Ancient Greek δέκα (déka)der. Proto-Indo-European *déḱm̥ Proto-Italic *dekəm Latin decemder. Esperanto dek Esperanto du Esperanto -a Esperanto okdek-dua From ok + dek + du + -a.