simoleon American slang, since c. 1830 A dollar. [ < British slang (since XVII but obsolete by late XIX) simon, a sixpence. There is no explanation of the British usage. Simon Magus sought to buy sacramental powers for money, and simony, named after him, is the sin of selling the services of the church for money. The money nexus is apparent, but no proper priest will sell out his office for a mere sixpence. Nor is there an explanation of the American variation. What is certain is that British simon passed into American simoleon, the monetary exchange rate shifting from British 6 p. to American $1.]
– Dictionary & Native’s Guide to the Unknown American Language