A confidence trick; specifically one which begins with the pretence that money has been found or otherwise acquired and that the victim can secure a share in it by paying a smaller sum.
Origin
1930s.
Definition of pigeon drop in US English:
pigeon drop
noun
US informal, criminals' slang
A confidence trick; specifically one which begins with the pretence that money has been found or otherwise acquired and that the victim can secure a share in it by paying a smaller sum.