The Greek Alphabet Letter CHI is the 22nd letter of the Greek alphabet. It is pronounced as a 'k' sound and is transliterated as 'kh'. CHI is also used in mathematics and science to represent the constant of an electric current. In physics, it is used to represent the angular velocity of a particle. In chemistry, it is used to represent the chemical symbol for chromium. In biology, it is used to represent the chirality of a molecule. CHI is also used in astrology to represent the planet Jupiter.