half-life

noun half-lives

1. The time required for half the nuclei in a sample of an isotope to undergo radioactive decay. "The guy that just left—what's he got in his lungs?" / "Well, I'm not very sure. But the two best candidates are uranium-233 and plutonium-239, one or both." / "They're in his bones too, aren't they?" / "Yeah, they're both boneseekers. And they've got half-lives of one hundred sixty-two thousand and
2. physical In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
3. The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity. For nonporous surfaces such as steel, in a dark and low-humidity environment, the CCP virus has an 18-hour half-life—the time required for it to decrease by half , according to the researchers' findings.
4. The amount of time it takes for an idea or a fashion to lose half of its influential power. Most books of scholarship have surprisingly short intellectual half-lives during which they make a difference"