Where does “σπαθίον” come from?

σπαθίον (Ancient Greek) comes from Ancient Greek σπάθη, from Proto-Indo-European sph₂-dʰ-.

Ancestry of “σπαθίον”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	σπάθη	any broad blade, of wood or metal
2	Proto-Indo-European	sph₂-dʰ-	—

σπαθίον — Etymology, Origin & Word History | Etymology Explorer