Where does “στοιχειώδης” come from?

στοιχειώδης (Greek) comes from Ancient Greek στοιχειώδης, from Ancient Greek στοιχεῖον, from Ancient Greek στοῖχος, from Proto-Hellenic stóikʰos, from Proto-Indo-European stóygʰ-os, from Proto-Indo-European steygʰ- — to go; to climb.

στοιχειώδης (Greek): basic, elementary; fundamental