1A document which represents a formal undertaking to pay a ransom for something, especially a captured ship (now historical).
2North American a banknote used to pay a ransom, especially one which is marked or has its serial number recorded, so as to aid in the tracing of the kidnappers.
Origin
Mid 18th century.
Definition of ransom bill in US English:
ransom bill
noun
1A document which represents a formal undertaking to pay a ransom for something, especially a captured ship (now historical).
2North American a banknote used to pay a ransom, especially one which is marked or has its serial number recorded, so as to aid in the tracing of the kidnappers.