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
So tee up your initiatives not as short-run campaigns with an implied half-life, but as the focal point of a permanent pivot toward a culture of continuous learning.
—
John Kannapell, Forbes.com, 14 Apr. 2025
Caffeine has a half-life of roughly five to six hours but can stay in your body longer.
—Elizabeth Barnes, Verywell Health, 19 Mar. 2025
The radioactive decay of carbon-14 is weak and has a half-life of 5,730 years.
—Ameya Paleja, Interesting Engineering, 14 Mar. 2025
Voters’ minds are fleeting and blame has a quick half-life in Washington.
—Philip Elliott, TIME, 14 Feb. 2025
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John Kannapell, Forbes.com, 14 Apr. 2025
Caffeine has a half-life of roughly five to six hours but can stay in your body longer.
—Elizabeth Barnes, Verywell Health, 19 Mar. 2025
The radioactive decay of carbon-14 is weak and has a half-life of 5,730 years.
—Ameya Paleja, Interesting Engineering, 14 Mar. 2025
Voters’ minds are fleeting and blame has a quick half-life in Washington.
—Philip Elliott, TIME, 14 Feb. 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 5 May. 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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