Green’s Dictionary of Slang

1. (US) a good idea, a scheme.

1947		B. Schulberg Harder They Fall (1971) 171: I gotta weenie for improving the take and you dial out on me.
1962		S. Longstreet Flesh Peddlers (1964) 232: It’s a device called the ‘gimmick,’ the ‘weenie.’.

2. a hidden catch.

1978

S. Longstreet Straw Boss (1979) 258: ‘What’s the weenie?’ ‘The what?’ ‘The catch!’ ‘Take what you like,’ my Mom always said, ‘and pay for it.’.