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
Those close to Khong marvel at the long half-life of her short stories.
—
Mariella Rudi, Los Angeles Times, 13 Apr. 2026
But still, David and I walk parallel paths in the long half-life of loss.
—Literary Hub, 13 Apr. 2026
Cesium 137 is highly soluble in water and has a half-life of 30 years, Alkis says.
—Stephanie Pappas, Scientific American, 10 Apr. 2026
Its short half-life, however, required it to be injected several times a day, which limited its appeal as a drug, and the company ran out of funding.
—Dhruv Khullar, New Yorker, 6 Apr. 2026
See All Example Sentences for half-life
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Mariella Rudi, Los Angeles Times, 13 Apr. 2026
But still, David and I walk parallel paths in the long half-life of loss.
—Literary Hub, 13 Apr. 2026
Cesium 137 is highly soluble in water and has a half-life of 30 years, Alkis says.
—Stephanie Pappas, Scientific American, 10 Apr. 2026
Its short half-life, however, required it to be injected several times a day, which limited its appeal as a drug, and the company ran out of funding.
—Dhruv Khullar, New Yorker, 6 Apr. 2026
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 17 Apr. 2026.
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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