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, because ketamine has a short half-life, the traces of the substance in his system couldn't have been from one of those treatment sessions, the report said.
—
Mekishana Pierre, Entertainment Weekly, 21 Oct. 2025
For the average person, caffeine has a half-life of about five hours.
—Carley Millhone, Health, 4 Oct. 2025
Iodine radioisotopes have half-lives that span from a tenth of a second to 16 million years.
—Andrea Richard, The Conversation, 2 Oct. 2025
One of the most popular, and notorious, alprazolam—more commonly known as Xanax—has a half-life of only twelve hours.
—P.e. Moskowitz
september 11, Literary Hub, 11 Sep. 2025
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Mekishana Pierre, Entertainment Weekly, 21 Oct. 2025
For the average person, caffeine has a half-life of about five hours.
—Carley Millhone, Health, 4 Oct. 2025
Iodine radioisotopes have half-lives that span from a tenth of a second to 16 million years.
—Andrea Richard, The Conversation, 2 Oct. 2025
One of the most popular, and notorious, alprazolam—more commonly known as Xanax—has a half-life of only twelve hours.
—P.e. Moskowitz
september 11, Literary Hub, 11 Sep. 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 25 Oct. 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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