- the 14th letter of the Greek alphabet (Ξ, ξ).
- the group of consonant sounds represented by this letter.
- the 14th letter in the Greek alphabet (Ξ, ξ), a composite consonant, transliterated as x
- a river in S China, rising in Yunnan province and flowing east to the Canton delta on the South China Sea: the main river system of S China. Length: about 1900 km (1200 miles)
