I. ˈ ̷ ̷ˌ ̷ ̷ noun
also half-life period
1. : the time required for half of the atoms of a radioactive substance present at the beginning to become disintegrated
rays from uranium have a half-life of millions of years — F.B.Colton
this isotope has half-life of twenty-three minutes — L.J.Levert
there will still be one quarter of the element left at the end of two half-life periods — G.E.Owen
2. : the time required for half the amount of a substance (as a drug or radioactive tracer) in or introduced into a living system to be eliminated whether by excretion, metabolic decomposition, or other natural process
II. noun
: a period of usefulness or popularity preceding decline or obsolescence
slang has a short half-life