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
Due to certain properties of berberine, such as its half-life and side effects, timing may be important in maximizing its benefits.
—
Emmanuella Ogbonna, Health, 26 Dec. 2025
Key Takeaways Nicotine has a half-life of about two hours and can stay in the blood for about one to three days.
—Heather Jones, Verywell Health, 30 Nov. 2025
Its half-life is a staggering 432 years, five times longer than plutonium-238.
—Kaif Shaikh, Interesting Engineering, 14 Nov. 2025
The radioactive half-life of plutonium-239, one of the remnants of US nuclear testing there, is 24,110 years.
—Brad Lendon, CNN Money, 4 Nov. 2025
See All Example Sentences for half-life
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.
Emmanuella Ogbonna, Health, 26 Dec. 2025
Key Takeaways Nicotine has a half-life of about two hours and can stay in the blood for about one to three days.
—Heather Jones, Verywell Health, 30 Nov. 2025
Its half-life is a staggering 432 years, five times longer than plutonium-238.
—Kaif Shaikh, Interesting Engineering, 14 Nov. 2025
The radioactive half-life of plutonium-239, one of the remnants of US nuclear testing there, is 24,110 years.
—Brad Lendon, CNN Money, 4 Nov. 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 5 Jan. 2026.
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
The Journal of the American Medical AssociationLove words? Need even more definitions?
Merriam-Webster unabridged
Share