1
: the time required for half of something to undergo a process: such as
a
: the time required for half of the atoms of a radioactive substance to become disintegrated
b
: the time required for half the amount of a substance (such as a drug, radioactive tracer, or pesticide) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
2
: a period of usefulness or popularity preceding decline or obsolescence
slang usually has a short half-life
Examples of half-life in a Sentence
Recent Examples on the Web
Which one to choose depends on several factors, including the isotope’s half-life and its decay energy.
—
IEEE Spectrum, 25 Aug. 2025
Its half-life can range from about one hour to up to five days.
—Ayesha Gulzar, Verywell Health, 25 Aug. 2025
At the time, Walmart issued a recall for three lots of frozen raw shrimp, determined to have low levels of the radioactive isotope, which has a half-life of about 30 years.
—Brenton Blanchet, People.com, 23 Aug. 2025
The autopsy report additionally noted that Perry had been receiving legal (though controversial) ketamine infusion treatment around the time of his death, but because ketamine has a short half-life, the traces of the substance in his system couldn't have been from one of those treatment sessions.
—Mekishana Pierre, EW.com, 18 Aug. 2025
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IEEE Spectrum, 25 Aug. 2025
Its half-life can range from about one hour to up to five days.
—Ayesha Gulzar, Verywell Health, 25 Aug. 2025
At the time, Walmart issued a recall for three lots of frozen raw shrimp, determined to have low levels of the radioactive isotope, which has a half-life of about 30 years.
—Brenton Blanchet, People.com, 23 Aug. 2025
The autopsy report additionally noted that Perry had been receiving legal (though controversial) ketamine infusion treatment around the time of his death, but because ketamine has a short half-life, the traces of the substance in his system couldn't have been from one of those treatment sessions.
—Mekishana Pierre, EW.com, 18 Aug. 2025
See All Example Sentences for half-life
Cite this Entry
“Half-life.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/half-life. Accessed 10 Sep. 2025.
Copy CitationMedical Definition
half-life
noun
ˈhaf-ˌlīf 
ˈhȧf-
: the time required for half of something to undergo a process: as
a
: the time required for half of the atoms of a radioactive substance to become disintegrated
b
: the time required for half the amount of a substance (as a drug or radioactive tracer) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes
the serum half-life is about 2 days—The Journal of the American Medical Association
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