/fit"nis/ , n.
1. health.
2. capability of the body of distributing inhaled oxygen to muscle tissue during increased physical effort.
3. Also called Darwinian fitness . Biol.
a. the genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring or close kin that survive to reproductive age.
b. the ability of a population to maintain or increase its numbers in succeeding generations.
[ 1570-80; FIT 1 + -NESS ]