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Noun: half-life (half-lives)  hãf lIf
  1. The time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
    "the half-life of humic acid is measured in centuries";
    - half life

Derived forms: half-lives

Type of: period, period of time, time period

Encyclopedia: Half-life, effective