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.
In most companies, great ideas have a vanishing half-life: A project team wraps a phase and notices a pattern, or a sales call reveals language that perfectly captures a client’s problem, but then… the idea fades. Maggie McGrath, Forbes.com, 23 May 2025 His efforts to blame everyone else for his own failures are sure to have a very short half-life. Michael Hiltzik, Los Angeles Times, 20 May 2025 In a Life Kit episode, sleep researcher Matthew Walker said that caffeine has a half-life of about six hours in most people. Malaka Gharib, NPR, 19 May 2025 More than half of big US cities don't use chlorine, in part because free chlorine in water is highly reactive and has a short half-life and can interact with other substances to create harmful compounds thought to be carcinogenic. Matthew Korfhage, Wired News, 16 May 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 29 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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