Greek alphabet glottal ("heth") was borrowed in two different functions by different dialects of Greek: as a letter for /h/ (Η, heta) by those dialects that had such a sound, and as an additional vowel letter for the long (Η, eta) by those dialects that lacked the consonant. Eventually, a seventh vowel letter for the long (Ω, omega) was introduced. Greek also introduced three new consonant letters for its aspirated plosive sounds and consonant clusters: Φ ("phi") for , Χ ("chi") for and Ψ ("psi") for . In western Greek variants, Χ was instead used for and Ψ for . The origin
Xi (letter) dialects of most of the Greek mainland and Euboea, the sound [ks] was represented by Χ (which in classical Greek is chi, used for ). Because this variant of the Greek alphabet was used in Italy, the Latin alphabet borrowed Χ rather than Ξ as the Latin letter X. While having no Latin derivative, the Xi was adopted into the early Cyrillic alphabet, as the letter ksi (Ѯ, ѯ). The uppercase letter Ξ is used as symbol for: The lowercase letter ξ is used as a symbol for: These characters are used only as mathematical symbols. Stylized Greek text should