Green’s Dictionary of Slang

not on a bet phr.

In phrases

not on a bet (phr.)

(US) under no circumstances.

1930
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1994
[US]M. Fiaschetti You Gotta Be Rough 63: The man they suspect wouldn’t squeal on a bet.
[US]S. Paige Maybe I’ll Pitch Forever 64: Not that I’d give up women, not on a bet.
[US]D.F. Wallace ‘Ticket to the Fair’ in Harper’s July 45/1: ‘Traish’ [sic] he calls the carnies. ‘Lowlifes.’ He gestures down at the twirling rides. ‘Wouldn’t let my own kids go off down there on a goddamn bet.’.