not on

not on (not comparable)

1. Unacceptable or impossible.
   • 1998, James P. Hogan, Bug Park, Chapter Twenty-four,

     It's just not on. We can't go breaking into another lawyer's office. I mean . . . it's just not something you can do.

   • 1998, Simon Blackburn, Ruling Passions: A Theory of Practical Reasoning, page 124,

     A feature of a situation may be influencing us although we do not realize it. From the agent's point of view the motivational power and direction of a consideration may not even be recognized. We often do not know why certain choices are just not on, and others so strangely attractive.

   • 2003, Dan Connell (author), Lionel Cliffe and Basil Davidson (introduction), Taking on the Superpowers: Collected Articles on the Eritrean Revolution, 1976-1982, page 325,

     After a week or so, he and I determined that walking hundreds of miles behind guerrilla lines under these conditions was just not on for him, and he packed his equipment to return home.

• “be not on” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.
• “not on” in the Collins English Dictionary, Glasgow: HarperCollins Publishers.