Chi (Greek letter) - Definition and Overview

Chi (upper case Χ, lower case χ) is the 22nd letter of the Greek alphabet. In the system of Greek numerals it has a value of 600. The 'ch' in 'chi' is a voiceless palatal fricative, which is prounounced like the 'ch' in German 'ich' or some variants of 'h' in the English 'human'.

The upper-case letter Χ is used as the symbol for:

• The name of Jesus Christ in Christianity, as in X-mas etc.

The lower-case letter χ is used as the symbol for:

• The chi-square distribution in statistics.
• The electric susceptibility in physics.
• The chromatic number of a graph in graph theory.
• The voiceless uvular fricative (IPA) in phonology.