chi 1 also khi (k?, k?)n. The 22nd letter of the Greek alphabet. See Table at alphabet.[Late Greek kh?, from earlier khei.]chi 2 also ch’i or qi (ch?)n. The vital force believed in Taoism and other Chinese thought to be inherent in all things. The unimpeded circulation of chi and a balance of its negative and positive forms in the body are held to be essential to good health in traditional Chinese medicine.[Mandarin qì, air, spirit, energy of life, from Middle Chinese khi`.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.