English

Noun

half-life ‎(plural half-lives)

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"

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