the minimum time necessary to excite a tissue, such as that of muscle or nerve cells, with an electric current of twice the rheobase
See chronaxie in American Heritage Dictionary 4
also chro·nax·y(krōˈnăkˌsē, krŏnˈăkˌ-)
nounpl.chro·nax·ies
The minimum interval of time necessary to electrically stimulate a muscle or nerve fiber, using twice the minimum current needed to elicit a threshold response.