Where does “ポリュムニアー” come from?

ポリュムニアー (Japanese) comes from Ancient Greek Πολύμνια, from Ancient Greek πολῠ́ς — many.

Ancestry of “ポリュムニアー”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Πολύμνια	—
2	Ancient Greek	πολῠ́ς	many