half-life

noun
\ ˈhaf-ˌlīf How to pronounce half-life (audio) , ˈhäf- \

Definition of half-life

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

First Known Use of half-life

1907, in the meaning defined at sense 1

Keep scrolling for more

Learn More about half-life

Time Traveler for half-life

Time Traveler

The first known use of half-life was in 1907

See more words from the same year

Statistics for half-life

Cite this Entry

“Half-life.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/half-life. Accessed 15 May. 2021.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

Keep scrolling for more

More Definitions for half-life

half-life

noun

English Language Learners Definition of half-life

technical : the time it takes for a radioactive substance to lose half its radioactivity

half-life

noun
\ ˈhaf-ˌlīf, ˈhäf- \
plural half-lives\ -​ˌlīvz \

Kids Definition of half-life

: the time required for half of the atoms of a radioactive substance to change composition

half-life

noun
\ -ˌlīf How to pronounce half-life (audio) \

Medical Definition of half-life

: 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 daysJournal of the American Medical Association

Comments on half-life

What made you want to look up half-life? Please tell us where you read or heard it (including the quote, if possible).

WORD OF THE DAY

Test Your Vocabulary

Words Used by Nabokov Quiz

  • image1676440788
  • Choose the best definition or synonym for the word in bold: "There are some eructations that sound like cheers—at least, mine did." Lolita
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ
Typeshift

Anagram puzzles meet word search.

TAKE THE QUIZ
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!