Present participle of heist; committing a robbery or theft, especially one that is large or dramatic.
From heist (variant of hoist) plus *-ing*. The gerund form describes the ongoing action of committing theft or robbery.
The shift from 'hoist' (lifting something) to 'heist' (stealing) to 'heisting' (actively robbing) is a great example of how verbs and their derivatives stick to an action's core meaning even as slang transforms it.
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