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
Voters’ minds are fleeting and blame has a quick half-life in Washington.
—
Philip Elliott, TIME, 14 Feb. 2025
The rare radioactive isotope produced by cosmic rays in the atmosphere, is used to date objects millions of years old, because its half-life is 1.4 million years.
—Paul Smaglik, Discover Magazine, 10 Feb. 2025
The remaining alcohol can take up to five half-lives (i.e. 20–25 hours) to be cleared completely.
—Angelica Bottaro, Verywell Health, 23 Jan. 2025
Image Celebrity status has a half-life, especially when much of your fan base consists of teenage boys.
—Bruce Schoenfeld, New York Times, 22 Jan. 2025
See all Example Sentences for half-life 
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Philip Elliott, TIME, 14 Feb. 2025
The rare radioactive isotope produced by cosmic rays in the atmosphere, is used to date objects millions of years old, because its half-life is 1.4 million years.
—Paul Smaglik, Discover Magazine, 10 Feb. 2025
The remaining alcohol can take up to five half-lives (i.e. 20–25 hours) to be cleared completely.
—Angelica Bottaro, Verywell Health, 23 Jan. 2025
Image Celebrity status has a half-life, especially when much of your fan base consists of teenage boys.
—Bruce Schoenfeld, New York Times, 22 Jan. 2025
See all Example Sentences for half-life
Dictionary Entries Near half-life
Cite this Entry
“Half-life.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/half-life. Accessed 21 Feb. 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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