X

In English orthography, ⟨x⟩ is typically pronounced as the voiceless consonant cluster /ks/ when it follows the stressed vowel (e.g. ox), and the voiced consonant /ɡz/ when it precedes the stressed vowel (e.g. exam). It is also pronounced /ɡz/ when it precedes a silent ⟨h⟩ and a stressed vowel (e.g. exhaust).[3] Before ⟨i⟩ or ⟨u⟩, it can be pronounced /kʃ/ or /ɡʒ/ (e.g. sexual and luxury); these result from earlier /ksj/ and /ɡzj/. It also makes the sound /kʃ/ in words ending in -xion (typically used only in British-based spellings of the language; American spellings tend to use -ction). When ⟨x⟩ ends a word, it is always /ks/ (e.g. fax), except in loan words such as faux (see French, below).

There are very few English words that start with ⟨x⟩ (the fewest of any letter). When ⟨x⟩ does start a word, it is usually pronounced /z/ (e.g. xylophone, xenophobia, and xanthan); in rare recent loanwords or foreign proper names, it can also be pronounced /s/ (e.g. the obsolete Vietnamese monetary unit xu) or /ʃ/ (e.g. Chinese names starting with Xi like Xiaomi or Xinjiang). Many of the words that start with ⟨x⟩ are of Greek origin, or standardized trademarks (Xerox) or acronyms (XC). In abbreviations, it can represent "trans-" (e.g. XMIT for transmit, XFER for transfer), "cross-" (e.g. X-ing for crossing, XREF for cross-reference), "Christ-" as shorthand for the labarum (e.g. Xmas for Christmas, Xian for Christian), the "crys-" in crystal (XTAL), or various words starting with "ex-" (e.g. XL for extra large, XOR for exclusive-or).

X is the third least frequently used letter in English (after ⟨q⟩ and ⟨z⟩), with a frequency of about 0.15% in words.[4]

In Latin, ⟨x⟩ stood for [ks]. In some languages, as a result of assorted phonetic changes, handwriting adaptations or simply spelling convention, ⟨x⟩ has other pronunciations:

• In Basque, ⟨x⟩ represents [ʃ]. Additionally there is the digraph ⟨tx⟩ [tʃ].
• In Dutch, ⟨x⟩ usually represents [ks], except in the name of the island of Texel, which is pronounced Tessel. This is because of historical sound-changes in Dutch, where all /ks/ sounds have been replaced by /s/ sounds. Words with an ⟨x⟩ in the Dutch language are nowadays usually loanwords. In the Dutch-speaking part of Belgium, family names with ⟨x⟩ are not uncommon (e.g. Dierckx, Hendrickx, Koninckx, Sterckx, Vranckx).
• In Norwegian, ⟨x⟩ is generally pronounced [ks], but since the 19th century, there has been a tendency to spell it out as ⟨ks⟩; it may still be retained in personal names, though it is fairly rare, and occurs mostly in foreign words and SMS language. Usage in Danish and Finnish is similar (while Swedish, on the other hand, makes frequent use of ⟨x⟩ in native words as well as in loanwords).
• In German, generally pronounced [ks]; in native words, however,such as Ochs or wachsen, the cluster [ks] is often written ⟨chs⟩.
• French: at the ends of words, silent (or [z] in liaison if the next word starts with a vowel). Three exceptions are pronounced [s]: six ("six"), dix ("ten") and in some city names such as Bruxelles (although some people pronounce it 'ks') or Auxerre; it is fully pronounced [ks] in Aix, the name of several towns. It is pronounced [z] in sixième and dixième. Otherwise [ks] or (primarily in words beginning with ex- followed by a vowel) [ɡz].
• In Italian, ⟨x⟩ is either pronounced [ks], as in extra, uxorio, xilofono,[5] or [ɡz], as exogamia, when it is preceded by ⟨e⟩ and followed by a vowel. In several related languages, notably Venetian, it represents the voiced sibilant [z]. It is also used, mainly amongst the young people, as a short written form for "per", meaning "for": for example, "x sempre" ("forever"). This is because in Italian the multiplication sign (similar to ⟨x⟩) is called "per". However, ⟨x⟩ is found only in loanwords, as it is not part of the standard Italian alphabet; in most words with ⟨x⟩, this letter may be replaced with 's' or 'ss' (with different pronunciation: xilofono/silofono, taxi/tassì) or, rarely, by 'cs' (with the same pronunciation: claxon/clacson).
• In Old Spanish, ⟨x⟩ was pronounced [ʃ], as it is still currently in other Iberian Romance languages. Later, the sound evolved to a hard [x] sound. In modern Spanish, due to a spelling reform, whenever ⟨x⟩ is used for the [x] sound it has been replaced with ⟨j⟩, including in words that originally had ⟨x⟩ such as ejemplo or ejercicio, though ⟨x⟩ is still retained for some names (notably 'México', even though 'Méjico' may sometimes be used in Spain). Presently, ⟨x⟩ represents the sound [s] (word-initially), or the consonant cluster [ks] (e.g. oxígeno, examen). Rarely, it can be pronounced [ʃ] as in Old Spanish in some proper nouns such as 'Raxel' (a variant of Rachel) and Uxmal.
• In Galician and Leonese, ⟨x⟩ is pronounced [ʃ] in most cases (often used in place of etymological g or j). The pronunciation [ks] occurs in learned words, such as 'taxativo' (taxing). However, Galician speakers tend to pronounce it [s], especially when it appears before plosives, such as in 'externo' (external).
• In Catalan, ⟨x⟩ has three sounds; the most common is [ʃ]; as in 'xarop' (syrup). Other sounds are: [ks]; 'fixar' (to fix), [ɡz]; 'examen'. In addition, [ʃ] gets voiced to [ʒ] before voiced consonants; 'caixmir'. Catalan also has the digraph ⟨tx⟩, pronounced [tʃ].
• In Portuguese, ⟨x⟩ has four main sounds; the most common is [ʃ], as in 'xícara' (cup). The other sounds are: [ks] as in 'flexão' (flexion); [s], when preceded by E and followed by a consonant, as in 'contexto' ([ʃ] in European Portuguese), and in a small number of other words, such as 'próximo' (close/next); and (the rarest) [z], which occurs in the prefix 'ex-' before a vowel, as in 'exagerado' (exaggerated). A rare fifth sound is [ɡz], coexisting with [z] and [ks] as acceptable pronunciations in exantema and in words with the Greek prefix 'hexa-'.
• In Sardinian and Ligurian, X represents [ʒ].
• In Venetian, it represents the voiced alveolar sibilant [z] much like in Portuguese 'exagerado', English 'xylophone' or in the French 'sixième'. Examples from medieval texts include raxon (reason), prexon (prison), dexerto (desert), chaxa/caxa (home). Nowadays, the best-known word is xe (is/are). The most notable exception to this rule is the name Venexia [veˈnɛsja] in which ⟨x⟩ has evolved from the initial voiced sibilant [z] to the present day voiceless sibilant.
• In Albanian, ⟨x⟩ represents [dz], while the digraph ⟨xh⟩ represents [dʒ].
• In Maltese, ⟨x⟩ is pronounced [ʃ] or, in some cases, [ʒ] (only in loanwords such as 'televixin', and not for all speakers).
• In Polish, ⟨x⟩ was used prior to 19th century both in loanwords and native words and was pronounced [ks] or [ɡz], e.g. xiążę, xięstwo (now książę, księstwo). Later was replaced by ⟨ks⟩ and ⟨gz⟩ in almost all words and remained only in a few loanwords as 'xenia' (xenien), surnames as Axentowicz, Jaxa, Koxowski, Mixtacki, Rexemowski, Xiężopolski, names as Xawery, Xymena and abbreviations.

Additionally, in languages for which the Latin alphabet has been adapted only recently, ⟨x⟩ has been used for various sounds, in some cases inspired by European usage, but in others, for consonants uncommon in Europe. For these no Latin letter stands out as an obvious choice, and since most of the various European pronunciations of ⟨x⟩ can be written by other means, the letter becomes available for more unusual sounds.

• ⟨x⟩ represents [x] (voiceless velar fricative) in e.g. Azerbaijani, Kurdish (Hawar alphabet), Georgian (when Latinized), Lojban, Pashto (when Latinized), Tatar (Jaꞑalif, Zamanälif, official romanization of 2012), Uzbek, and Uyghur (Latin script).
• Esperanto: The x-convention replaces ⟨ĉ⟩, ⟨ĝ⟩, ⟨ĥ⟩, ⟨ĵ⟩, ⟨ŝ⟩, and ⟨ŭ⟩ with x-suffixes: ⟨cx⟩, ⟨gx⟩, ⟨hx⟩, ⟨jx⟩, ⟨sx⟩, and ⟨ux⟩.
• In transliteration of Indian languages, primarily Indo-Aryan languages, ⟨x⟩ represents the consonant cluster [kʃ] in alternate spellings of words containing 'क्ष' (kṣ), especially names such as Laxmi and Dixit. Less frequently, ⟨x⟩ is used to represent 'ख़' [x].
• In Apache ⟨x⟩ represents [x]
• In Nahuatl, ⟨x⟩ represents [ʃ].
• In Nguni languages, ⟨x⟩ represents the alveolar lateral click [ǁ].
• In Pirahã, ⟨x⟩ symbolizes the glottal stop [ʔ].
• An illustrating example of "x" as a "leftover" letter is differing usage in three different Cushitic languages:
  • Afar: voiced alveolar implosive [ɗ]
  • Oromo: alveolar ejective [tʼ]
  • Somali: voiceless pharyngeal fricative [ħ]
• In East and Asia:
  • In Lao, based on romanization of Lao consonants, ⟨x⟩ may represent [ɕ], e.g. in Lan Xang.
  • In Vietnamese, ⟨x⟩ is pronounced like English ⟨s⟩ (at the beginning of a word, e.g. "sing"). This sound was [ɕ] in Middle Vietnamese, resembling the Portuguese sound /ʃ/, spelled ⟨x⟩.
  • In Hanyu Pinyin, Standard Chinese's official transcription system in China, Malaysia, Singapore, and Taiwan, the letter ⟨x⟩ represents the voiceless alveolo-palatal fricative /ɕ/, for instance in 'Xi', [ɕi].
  • In Sylheti {x} is pronounced like Arabic خ [kh]

In the International Phonetic Alphabet, ⟨x⟩ represents a voiceless velar fricative.

• X with diacritics: Ẍ ẍ Ẋ ẋ X̂ x̂ ᶍ[14]
• IPA-specific symbols related to X: χ
• Teuthonista phonetic transcription-specific symbols related to X:[15]
  • U+AB56 ꭖ LATIN SMALL LETTER X WITH LOW RIGHT RING
  • U+AB57 ꭗ LATIN SMALL LETTER X WITH LONG LEFT LEG
  • U+AB58 ꭘ LATIN SMALL LETTER X WITH LONG LEFT LEG AND LOW RIGHT RING
  • U+AB59 ꭙ LATIN SMALL LETTER X WITH LONG LEFT LEG WITH SERIF
• ˣ : Modifier letter small x is used for phonetic transcription
• ₓ : Subscript small x is used in Indo-European studies[16]

• Χ χ : Greek letter Chi, from which the following derive:
  • Х х : Cyrillic letter Kha
  • Ⲭ ⲭ : Coptic letter Khe, which derives from Greek Chi
  • 𐍇 : Gothic letter enguz, which derives from Greek Chi
  • 𐌗 : Old Italic X, which derives from Greek Chi, and is the ancestor of modern Latin X
    • ᚷ : Runic letter Gyfu, which may derive from old Italic X
• Ξ ξ : Greek letter Xi, which was used in place of Chi in the Eastern (and the modern) Greek alphabets

¹ Also for encodings based on ASCII, including the DOS, Windows, ISO-8859 and Macintosh families of encodings.

In the C programming language, "x" preceded by zero (as in 0x or 0X) is used to denote hexadecimal literal values.

X is commonly used as a prefix term in nouns related to the X Window System and Unix[2]