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
Meanwhile other nations are pursuing or preserving their own RPS capabilities, with Europe’s sights set on americium 241, a radioisotope with a five-times-longer half-life but a five-times-weaker energy output than plutonium 238.
—
Hannah Richter, Scientific American, 13 Aug. 2025
Rooker adds that early studies suggest that E4 has a stable half-life suitable for once-daily oral dosing and a gentler impact on the liver compared to other estrogen formulations.
—Lauryn Higgins, Flow Space, 25 July 2025
This phenomenon is largely due to levodopa’s short half-life, which causes fluctuating levels of the drug in the bloodstream.
—New Atlas, 13 July 2025
The mobile space race and its half-life have significantly reduced.
—Zak Doffman, Forbes.com, 8 July 2025
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Hannah Richter, Scientific American, 13 Aug. 2025
Rooker adds that early studies suggest that E4 has a stable half-life suitable for once-daily oral dosing and a gentler impact on the liver compared to other estrogen formulations.
—Lauryn Higgins, Flow Space, 25 July 2025
This phenomenon is largely due to levodopa’s short half-life, which causes fluctuating levels of the drug in the bloodstream.
—New Atlas, 13 July 2025
The mobile space race and its half-life have significantly reduced.
—Zak Doffman, Forbes.com, 8 July 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 21 Aug. 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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