The story
- Anglo-Norman · derived frombullion
- Middle English · inherited frombulloin
- English todaybullion
From Middle English bulloin, bullioun, from Anglo-Norman bullion, of obscure origin, perhaps from French bouillon, extending the sense to that of ‘melting’. Middle Dutch boelioen (“base metal”) seems to have come from the unrelated French billon.
Etymology from Wiktionary, CC BY-SA 4.0.