Cambridge Dictionaries online Cambridge Dictionaries online

The most popular online dictionary and thesaurus for learners of English

English definition of “half-life”

half-life

noun [C usually sing]  /ˈhæfˌlɑɪf/ us  
physics, earth science the amount of time needed for the radioactivity (= harmful form of energy) of a radioactive substance to be reduced by half
(Definition of half-life from the Cambridge Academic Content Dictionary © Cambridge University Press)
What is the pronunciation of half-life?
Add Cambridge dictionaries to your browser to your website

Definitions of “half-life” in other dictionaries

Translations of “half-life”

Word of the Day

throw

to send something through the air with force, especially by a sudden movement of the arm

Word of the Day

Blog

Read our blog about how the English language behaves.

Learn More

New Words

Find words and meanings that have just started to be used in English, and let us know what you think of them.

Learn More