half-life

noun

ˈhaf-ˌlīf How to pronounce half-life (audio)
ˈhäf-
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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The lizard hormone half-life was nearly 100 times longer (~2.5 hours) which led to more research focusing on increasing half-life, resisting degradation and enhancing binding to the GLP-1 receptor. Lipi Roy, Forbes.com, 6 May 2025 For instance, experiments have shown the proton to be so stable that its half-life must be at least a hundred trillion trillion times the age of the universe. Lyndie Chiou, Scientific American, 30 Apr. 2025 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 See All Example Sentences for half-life

Word History

First Known Use

1907, in the meaning defined at sense 1

Time Traveler
The first known use of half-life was in 1907

Browse Nearby Words

Cite this Entry

“Half-life.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/half-life. Accessed 25 May. 2025.

Kids Definition

half-life

noun
-ˌlīf
: the time required for half of the atoms of a radioactive substance to change composition

Medical Definition

half-life

noun
ˈhaf-ˌlīf How to pronounce half-life (audio)
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 daysThe Journal of the American Medical Association
Last Updated: - Updated example sentences
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