Where does “doblon” come from?

doblon (English) comes from Spanish doblón, from Spanish doble, from Latin dūplus, from Proto-Italic *duplos — double.

Ancestry of “doblon”, step by step

Step	Language	Word	Meaning
1	Spanish	doblón	doubloon
2	Spanish	doble	double; twofold; double, twice as much
3	Latin	dūplus	double (twice as much, or as big)
4	Proto-Italic	*duplos	double