half-life
Technical term in physics and chemistry for the time required for a quantity to reduce to half its initial value, most commonly used for radioactive decay.
The half-life of uranium-238 is about 4.5 billion years.
The plasma half-life of this drug is short.
Compound of 半減 (hangen, 'halving') + 期 (ki, 'period'). The term is a direct translation of the English 'half-life'.