half-life
Say it: HAAF-life /ˈhɑːflaɪf/ · noun
What “half-life” means
The time needed for an amount to fall by half.
More precisely: The time it takes for half of a radioactive substance to decay, or for anything's effect to halve.
Example: “Caffeine has a half-life of about five hours, so that 4 p.m. coffee is still working at 9.”
When to use it
In science or careful explanations, for how long a substance takes to halve through decay or removal.
Similar words
decay time, lifespan
Quick check
A medicine's amount in your body drops from a full dose to half in eight hours. What is that interval?
its shelf life or its half-life?
Show the answer
its half-life
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