In the Greek alphabet, the letter ‘X’ corresponds to the letter ‘Chi’ (Χ, χ). Chi is the 22nd letter of the Greek alphabet and is pronounced like the English pronunciation of ‘K’ or ‘CH’ in some contexts.
Chi resembles the Latin letter ‘X’ in its uppercase form, although the lowercase version, ‘χ’, looks quite different. In ancient Greek, it held various phonetic values depending on the word and region. Chi is still commonly used in mathematics and science to denote variables or specific constants.