American English

Definition of critical mass noun from the Oxford Advanced American Dictionary

     

    critical mass

     noun
    noun
     
    [countable, uncountable]
     
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  1. 1(physics) the smallest amount of a substance that is needed for a nuclear chain reaction to take place
  2. 2the smallest size or amount of something that is needed for an effect or action to take place The new device already has a critical mass of users. I don't think we've reached critical mass for this particular law yet.
See the Oxford Advanced Learner's Dictionary entry: critical mass