Where does “*plūmā” come from?

*plūmā (Proto-Germanic) comes from Latin prūnum, from Ancient Greek προῦνον, from Ancient Greek προῦμνον — A plum fruit.

Ancestry of “*plūmā”, step by step

Step	Language	Word	Meaning
1	Latin	prūnum	—
2	Ancient Greek	προῦνον	—
3	Ancient Greek	προῦμνον	A plum fruit