Where does “triskaidecahedron” come from?

triskaidecahedron (English) comes from English -hedron, from Ancient Greek ἕδρα, from Proto-Hellenic *hédrā.

Ancestry of “triskaidecahedron”, step by step

Step	Language	Word	Meaning
1	English	-hedron	"Forms the names of solid figures bounded by a...
2	Ancient Greek	ἕδρα	seat, chair, stool, bench; the act of sitting;...
3	Proto-Hellenic	*hédrā	—