half-life

noun

ˈhaf-ˌlīf 

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

Are they doomed to live half-lives, gauged in literal length or internal fulfillment, always under the thumb of one boss or another? —Ben Travers, IndieWire, 12 Dec. 2024

Here’s everything to know about winterizing your vehicle as the weather cools across the state: Battery: Check its age and charge Anyone who has lived and driven in Phoenix long enough knows that car batteries have a half-life in America’s hottest big city. —Hayleigh Evans, The Arizona Republic, 7 Dec. 2024

These medications have long half-lives, says Katherine Saunders, MD, an obesity specialist at Weill Cornell Medicine in New York City and a cofounder of FlyteHealth. —Adam Gilden, Md, EverydayHealth.com, 6 Dec. 2024

Carbon-14 has a half-life of about 5,730 years, meaning the battery can theoretically last thousands of years, with diminishing output over time. —Jess Thomson, Newsweek, 5 Dec. 2024

Word History

First Known Use

1907, in the meaning defined at sense 1

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 

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