# X

X or x is the 24th and third-to-last letter in the modern English alphabet and the ISO basic Latin alphabet. Its name in English is ex (pronounced ), plural exes.

## History

In Ancient Greek, 'Χ' and 'Ψ' were among several variants of the same letter, used originally for and later, in western areas such as Arcadia, as a simplification of the digraph 'ΧΣ' for . In the end, more conservative eastern forms became the standard of Classical Greek, and thus 'Χ' (Chi) stood for (later ; palatalized to in Modern Greek before front vowels). However, the Etruscans had taken over 'Χ' from western Greek, and it therefore stands for in Etruscan and Latin.

The letter 'Χ' ~ 'Ψ' for was a Greek addition to the alphabet, placed after the Semitic letters along with phi 'Φ' for .

## Use in writing systems

### English

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

There are very few English words that start with (the fewest of any letter). When does start a word, it is usually pronounced (e.g. xylophone, xenophobia, and xanthan); in rare recent loanwords or foreign proper names, it can also be pronounced (e.g. the obsolete Vietnamese monetary unit xu) or (e.g. Chinese names starting with Xi like Xiaomi or Xinjiang). Many of the words that start with 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 and ), with a frequency of about 0.15% in words.

### Other languages

In Latin, stood for . In some languages, as a result of assorted phonetic changes, handwriting adaptations or simply spelling convention, has other pronunciations:
• In Basque, represents . Additionally there is the digraph .
• In Dutch, usually represents , except in the name of the island of Texel, which is pronounced Tessel. This is because of historical sound-changes in Dutch, where all sounds have been replaced by sounds. Words with an in the Dutch language are nowadays usually loanwords. In the Dutch-speaking part of Belgium, family names with are not uncommon (e.g. Dierckx, Hendrickx, Koninckx, Sterckx, Vranckx).
• In Norwegian, is generally pronounced , but since the 19th century, there has been a tendency to spell it out as ; 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 in native words as well as in loanwords).
• In German, generally pronounced ; in native words, however,such as Ochs or wachsen, the cluster is often written .
• at the ends of words , silent (or in liaison if the next word starts with a vowel). Three exceptions are pronounced : six ("six"), dix ("ten") and in some city names such as Bruxelles (although some people pronounce it 'ks') or Auxerre; it is fully pronounced in Aix, the name of several towns. It is pronounced in sixième and dixième. Otherwise or (primarily in words beginning with ex- followed by a vowel) .
• In Italian, is either pronounced , as in extra, uxorio, xilofono, or , as exogamia, when it is preceded by and followed by a vowel. In several related languages, notably Venetian, it represents the voiced sibilant . 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 ) is called "per". However, is found only in loanwords, as it is not part of the standard Italian alphabet; in most words with , 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, was pronounced , as it is still currently in other Iberian Romance languages. Later, the sound evolved to a hard sound. In modern Spanish, due to a spelling reform, whenever is used for the sound it has been replaced with , including in words that originally had such as ejemplo or ejercicio, though is still retained for some names (notably 'México', even though 'Méjico' may sometimes be used in Spain). Presently, represents the sound (word-initially), or the consonant cluster (e.g. oxígeno, examen). Rarely, it can be pronounced as in Old Spanish in some proper nouns such as 'Raxel' (a variant of Rachel) and Uxmal.
• In Galician and Leonese, is pronounced in most cases. In learned words, such as 'taxativo' (taxing), it is pronounced . However, Galician speakers tend to pronounce it , especially when it appears before plosives, such as in 'externo' (external).
• In Catalan, has three sounds; the most common is ; as in 'xarop' (syrup). Other sounds are: ; 'fixar' (to fix), ; 'examen'. In addition, gets voiced to before voiced consonants; 'caixmir'. Catalan also has the digraph , pronounced .
• In Portuguese, has four main sounds; the most common is , as in 'xícara' (cup). The other sounds are: as in 'flexão' (flexion); , when preceded by E and followed by a consonant, as in 'contexto' ( in European Portuguese), and in a small number of other words, such as 'próximo' (close/next); and (the rarest) , which occurs in the prefix 'ex-' before a vowel, as in 'exagerado' (exaggerated). A rare fifth sound is , coexisting with and as acceptable pronunciations in exantema and in words with the Greek prefix 'hexa-'.
• In Venetian, it represents the voiced alveolar sibilant 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 in which has evolved from the initial voiced sibilant to the present day voiceless sibilant.
• In Albanian, represents , while the digraph represents .
• In Maltese, is pronounced or, in some cases, (only in loanwords such as 'televixin', and not for all speakers).
• In Polish, was used prior to 19th century both in loanwords and native words and was pronounced or , e.g. xiążę, xięstwo (now książę, księstwo). Later was replaced by and 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, 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 can be written by other means, the letter becomes available for more unusual sounds.
• represents (voiceless velar fricative) in e.g. Azerbaijani, Kurdish (Hawar alphabet), Lojban, Tatar (Jaꞑalif, Zamanälif, official romanization of 2012), Uzbek, and Uyghur (Latin script).
• Esperanto: The x-convention replaces , , , , , and with x-suffixes: , , , , , and .
• In transliteration of Indian languages, primarily Indo-Aryan languages, represents the consonant cluster in alternate spellings of words containing 'क्ष' (kṣ), especially names such as Laxmi and Dixit. Less frequently, is used to represent 'ख़' .
• In Apache represents
• In Nahuatl, represents .
• In Nguni languages, represents the alveolar lateral click .
• In Pirahã, symbolizes the glottal stop .
• An illustrating example of "x" as a "leftover" letter is differing usage in three different Cushitic languages:
• Afar: voiced alveolar implosive
• Oromo: alveolar ejective
• Somali: voiceless pharyngeal fricative
• In East and Southeast Asia:
• In Lao, based on romanization of Lao consonants, may represent , e.g. in Lan Xang.
• In Vietnamese, is pronounced like English (at the beginning of a word, e.g. "sing"). This sound was in Middle Vietnamese, resembling the Portuguese sound , spelled .
• In Hanyu Pinyin, Standard Chinese's official transcription system in China, Malaysia, Singapore, and Taiwan, the letter represents the voiceless alveolo-palatal fricative , for instance in 'Xi', .

### Other systems

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

## Other uses

In mathematics, x is commonly used as the name for an independent variable or unknown value. The modern tradition of using x to represent an unknown was introduced by René Descartes in La Géométrie (1637). As a result of its use in algebra, X is often used to represent unknowns in other circumstances (e.g. X-rays, Generation X, The X-Files, and The Man from Planet X; see also Malcolm X).

On some identification documents, the letter X represents a non-binary gender, where F means female and M means male.

In the Cartesian coordinate system, x is used to refer to the horizontal axis.

It may also be used as a typographic approximation for the multiplication sign. In mathematical typesetting, x meaning an algebraic variable is normally in italic type ($x!$), partly to avoid confusion with the multiplication symbol. In fonts containing both x (the letter) and × (the multiplication sign), the two glyphs are dissimilar.

It can be used as an abbreviation for 'between' in the context of historical dating; e.g., '1483 x 1485'.

Maps and other images sometimes use an X to label a specific location, leading to the expression "X marks the spot".

The Roman numeral Ⅹ represents the number 10.

In art or fashion, the use of X indicates a collaboration by two or more artists, e.g. Aaron Koblin x Takashi Kawashima. This application, which originated in Japan, now extends to other kinds of collaboration outside the art world. This usage mimics the use of a similar mark in denoting botanical hybrids, for which scientifically the multiplication sign (×) is used, but informally a lowercase "x" is also used.

## Related characters

### Descendants and related characters in the Latin alphabet

• X with diacritics: Ẍ ẍ Ẋ ẋ
• IPA-specific symbols related to X:
• Teuthonista phonetic transcription-specific symbols related to X:
• ˣ : Modifier letter small x is used for phonetic transcription
• ₓ : Subscript small x is used in Indo-European studies

### Ancestors and siblings in other alphabets

• Χ χ : Greek letter Chi, from which the following derive:
• Х х : Cyrillic letter Kha
• : Coptic letter Khe, which derives from Greek Chi
• : 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
• : 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

## Computing

### Computing codes

:

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

### Operating systems

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