/haf"luyf', hahf"-/ , n. , pl. half-lives /-luyvz'/ .
1. Physics. the time required for one half the atoms of a given amount of a radioactive substance to disintegrate.
2. Pharm. the time required for the activity of a substance taken into the body to lose one half its initial effectiveness.
3. Informal. a brief period during which something flourishes before dying out.
Also, half life, halflife . Also called half-life period .
[ 1905-10; HALF + LIFE ]