half-life
noun/ˈhɑːf laɪf/
/ˈhæf laɪf/
[countable]- (physics) the time taken for the radioactivity of a substance to fall to half its original value
（放射性物质的）半衰期 - (biology) the time taken for the amount of a drug or other substance in the body to fall to half its original level
（体内物质的）半衰期