chi  
noun 
  (energy)     
  [ U ] medical uk/tʃiː/ us/tʃiː/ (or qi)气(中医理论中人体内最重要的能量) 
in some systems of Chinese medicine and exercise, the most important energy that a person has
   (letter)     
 [ C or U ] language, mathematics, science /kaɪ/ /kaɪ/(希腊语字母表的第22个字母) 
the 22nd letter of the Greek alphabet