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Half-life

//ˈhæfˌlaɪf// noun

Noun

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 twenty-four thousand years respectively. So they stay hot for a long time.""
2
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) wordnet
3
In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value. physical
4
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."
5
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""

From half- + life.

Unscramble this word: halflife