名詞 half life:

1. the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)
   同義詞：half-life

1. He's been lucky all his life and has never had to find out how the other half lives.
   他享了一輩子的福，從來不知道窮人生活的滋味。