Where does “oktaeder” come from?

oktaeder (Danish) comes from Ancient Greek ἕδρα, from Proto-Hellenic *hédrā.

oktaeder (Danish): octahedron

Definitions

Step	Language	Word	Meaning
1	Ancient Greek	ἕδρα	seat, chair, stool, bench; the act of sitting;...
2	Proto-Hellenic	*hédrā	—