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

Dioxins have a half-life in the body of seven to 11 years, according to the World Health Organization, and lead can also be undetectable in blood but still remain in the body, bound to bones, for decades. — Angus Chen, STAT, 22 July 2026

The doctor advised her to expect additional digestive issues for weeks because of the medication's long half-life, according to the essay. — Angelique Brenes, PEOPLE, 6 June 2026

And because none of the new skills were built on top of existing strengths, their half-life is short. — Vibhas Ratanjee, Forbes.com, 29 May 2026

Alan Cummings, a co-investigator on Voyager, told an audience in October 2024 that, technically, the probes' power will never run out because nuclear energy always has a half-life. — Elizabeth Howell, Space.com, 9 May 2026

Word History

First Known Use

1907, in the meaning defined at sense 1

Rhymes for half-life

• alewife
• birdlife
• folklife
• housewife
• jackknife
• midlife
• midwife
• nightlife
• penknife
• wildlife
• afterlife
• pocketknife

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