• (America) IPA: /ˈhæfˌlaɪf/


  1. (physics) The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.
  2. (chemistry) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
  3. (medicine) The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
  4. The time it takes for an idea or a fashion to lose half of its influential power.
    • 1991, Robert Ackerman, Introduction to Jane Ellen Harrison's Prolegomena to the Study of Greek Religion (1903)
      Most books of scholarship have surprisingly short intellectual 'half-lives during which they make a difference"
  • French: demi-vie
  • German: Halbwertszeit
  • Italian: emivita, semivita
  • Portuguese: meia-vida
  • Russian: пери́од полураспа́да
  • Spanish: periodo de semidesintegración; semivida, vida media
Translations Translations
  • Russian: период

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