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From the thematic Oxford Dictionary of Slang by Lexicographer John Ayto (including the word mark you already mention).

For a simple swindle:

fly-flat (1864) British, dated; applied to someone taken in by confidence tricksters; from fly (knowing, alert) + obsolete flat (gullible person)
- Joyce Cary: 'I don't see why we should consider the speculators.' 'A lot of fly-flats who thought they could beat us at the game.'(1938)

mark (1883) Orig US; applied to the intended victim of confidence tricksters; often in the phrase a soft (or easy) mark
Edmund McGirr: In the twenties it was the Yanks who was the suckers, but now... it's us who are the marks. (1973)

For kidnap victims:

package (1933) Mainly US; applied to a kidnap victim
• Sun (Baltimore): The 'package', as the kidnapped victim is called, is rushed across the State line and delivered to the'keepers'. (1933)

From the thematic Oxford Dictionary of Slang by Lexicographer John Ayto (including the word mark you already mention).

For a simple swindle:

fly-flat (1864) British, dated; applied to someone taken in by confidence tricksters; from fly (knowing, alert) + obsolete flat (gullible person)
- Joyce Cary: 'I don't see why we should consider the speculators.' 'A lot of fly-flats who thought they could beat us at the game.'(1938)

mark (1883) Orig US; applied to the intended victim of confidence tricksters; often in the phrase a soft (or easy) mark Edmund McGirr: In the twenties it was the Yanks who was the suckers, but now... it's us who are the marks. (1973)

For kidnap victims:

package (1933) Mainly US; applied to a kidnap victim
• Sun (Baltimore): The 'package', as the kidnapped victim is called, is rushed across the State line and delivered to the'keepers'. (1933)

From the thematic Oxford Dictionary of Slang by Lexicographer John Ayto (including the word mark you already mention).

For a simple swindle:

fly-flat (1864) British, dated; applied to someone taken in by confidence tricksters; from fly (knowing, alert) + obsolete flat (gullible person)
Joyce Cary: 'I don't see why we should consider the speculators.' 'A lot of fly-flats who thought they could beat us at the game.'(1938)

mark (1883) Orig US; applied to the intended victim of confidence tricksters; often in the phrase a soft (or easy) mark
Edmund McGirr: In the twenties it was the Yanks who was the suckers, but now... it's us who are the marks. (1973)

For kidnap victims:

package (1933) Mainly US; applied to a kidnap victim
• Sun (Baltimore): The 'package', as the kidnapped victim is called, is rushed across the State line and delivered to the'keepers'. (1933)

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source | link

From the thematic Oxford Dictionary of Slang by Lexicographer John Ayto (including the word mark you already mention).

For a simple swindle:

fly-flat (1864) British, dated; applied to someone taken in by confidence tricksters; from fly (knowing, alert) + obsolete flat (gullible person)
- Joyce Cary: 'I don't see why we should consider the speculators.' 'A lot of fly-flats who thought they could beat us at the game.'(1938)

mark (1883) Orig US; applied to the intended victim of confidence tricksters; often in the phrase a soft (or easy) mark • Edmund McGirr: In the twenties it was the Yanks who was the suckers, but now... it's us who are the marks. (1973)

For kidnap victims:

package (1933) Mainly US; applied to a kidnap victim
• Sun (Baltimore): The 'package', as the kidnapped victim is called, is rushed across the State line and delivered to the'keepers'. (1933)