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
However, the medical examiner wrote the ketamine in his system at death could not have been from that infusion therapy, as ketamine's half-life is three to four hours or less.
—
Alex Stone, ABC News, 15 Aug. 2024
However, per the autopsy, because of the drug's short half-life, the ketamine found in his system could not have come from his last therapy session, which occurred more than a week before his death.
—Shania Russell, EW.com, 15 Aug. 2024
About 40 percent of the radioactivity comes from the element cesium-137, which has a half-life of 30 years, meaning its radioactivity is reduced by half every 30 years.
—Philip Diehl, The Mercury News, 12 Aug. 2024
Metronidazole has a half-life of about eight hours.
—Alex Yampolsky, Verywell Health, 8 Aug. 2024
See all Example Sentences for half-life 
Alex Stone, ABC News, 15 Aug. 2024
However, per the autopsy, because of the drug's short half-life, the ketamine found in his system could not have come from his last therapy session, which occurred more than a week before his death.
—Shania Russell, EW.com, 15 Aug. 2024
About 40 percent of the radioactivity comes from the element cesium-137, which has a half-life of 30 years, meaning its radioactivity is reduced by half every 30 years.
—Philip Diehl, The Mercury News, 12 Aug. 2024
Metronidazole has a half-life of about eight hours.
—Alex Yampolsky, Verywell Health, 8 Aug. 2024
See all Example Sentences for half-life
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“Half-life.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/half-life. Accessed 19 Sep. 2024.
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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