Definition of before you can say knife in English:

before you can say knife

phrase

informal
  • Very quickly; almost instantaneously.

    • ‘The days rolled by in the camp - they were over before you could say knife.’
    soon, very soon, in a second, in a minute, in a moment, in a trice, in a flash, shortly, any second, any minute, any minute now, in a short time, in an instant, in less than no time, in no time at all, in next to no time, before you know it, before long
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