I. ˈkī, ˈkē noun
Etymology: Greek chei, chi
Date: 15th century
: the 22d letter of the Greek alphabet — see alphabet table
II. noun
or ch'i also qi ˈchē
Usage: often capitalized
Etymology: Chinese (Beijing) qì, literally, air, breath
Date: 1850
: vital energy that is held to animate the body internally and is of central importance in some Eastern systems of medical treatment (as acupuncture) and of exercise or self-defense (as tai chi)