X

This article is about the letter. For other uses, see X (disambiguation).

Not to be confused with multiplication sign.

ISO basic Latin alphabet
Aa	Bb	Cc	Dd
Ee	Ff	Gg	Hh
Ii	Jj	Kk	Ll
Mm	Nn	Oo	Pp
Qq	Rr	Ss	Tt
Uu	Vv	Ww	Xx
Yy	Zz

X ( /ˈɛks/; named ex, plural exes) is the twenty-fourth letter in the ISO basic Latin alphabet.

Uses

In mathematics, x is commonly used as the name for an independent variable or unknown value. The usage of x to represent an independent or unknown variable can be traced back to the Arabic word šay' شيء = “thing,” used in Arabic algebra texts such as the Al-Jabr. It was subsequently taken into Old Spanish with the pronunciation /ʃei/, which was written xei and soon habitually abbreviated to x. (The Spanish pronunciation of ⟨x⟩ has changed since.) This started the habit of using letters to represent quantities in algebra.^{[citation needed]}

It may also be used to signify the multiplication operation when a more appropriate glyph is unavailable. In mathematics, an "italicized x" ($x\!$) is often used to avoid potential confusion with the multiplication symbol. Another usage of X in mathematics is $\times$ which is used to represent the cross product.

Other non-mathematical uses include:

• As a result of its use in math, X is often used to represent unknowns in other circumstances (e.g. Person X, Place X, etc.; see also Malcolm X).
• X-rays are so called because their discoverer did not know what they were.
• X has been used as a namesake for a generation of humans: Generation X, commonly abbreviated to Gen X. It is the generation born after the baby boom ended, ranging from 1961 to 1981.
• It is commonly used in correspondence along with the letter O to indicate affection (as in "XOXO" - the Xs representing kisses and the Os hugs).
• X is also used for referring to 'the end of conversation'.
• X is used by the illiterate in lieu of a signature and indicates a signature line on forms.
• In cartoons, Xs are drawn instead of eyes to indicate the death of a character.
• X is commonly used as a generic mark (selecting an item on a form, indicating a location on a map, etc.).

History

In Ancient Greek, ⟨Χ⟩ and ⟨Ψ⟩ were among several variants of the same letter, used originally for /kʰ/ and later, in western areas such as Arcadia, as a simplification of the digraph ⟨ΧΣ⟩ for /ks/. In the end, more conservative eastern forms became the standard of Classical Greek, and thus ⟨Χ⟩ (Chi) stands for /kʰ/ (later /x/). However, the Etruscans had taken over ⟨Χ⟩ from western Greek, and it therefore stands for /ks/ in Etruscan and Latin.

The letter ⟨Χ⟩ ~ ⟨Ψ⟩ for /kʰ/ was a Greek addition to the alphabet, placed after the Semitic letters along with phi ⟨Φ⟩ for /pʰ/. (The variant ⟨Ψ⟩ later replaced the digraph ⟨ΦΣ⟩ for /ps/; omega was a later addition.) There has been much mostly fruitless debate about the origins of these added letters.

Greek Xi	Etruscan X

Usage

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

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:

• Basque: as a spelling for [ʃ]. Additionally there is the digraph tx [tʃ].
• Dutch: X usually represents [ks], except when it's used for the island of Texel, which is pronounced Tessel. This is because of a historical sound-changes in Dutch, where all -x- sounds have been replaced with -s- sounds. Words with an -x- in the Dutch language are nowadays usually loanwords.
• English: X is typically a sign for the compound consonants [ks]; or sometimes when followed by an accented syllable beginning with a vowel, or when followed by silent h and an accented vowel [ɡz] (e.g. exhaust, exam); usually [z] at the beginnings of words (e.g. xylophone, Xenon), and in some compounds keeps the [z] sound, as in (e.g. meta-xylene). 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). Before i or u it can also represent the sounds [ɡʒ] or [kʃ], for example, in the words luxury and sexual, respectively: these result from earlier [ɡzj] and [ksj]. Final x is always [ks] (e.g. ax/axe) except in loan words such as faux (see French, below).
  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 short hand 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).
  There are very few English words that start with X – the least amount of any letter. Many of the words that do start with X are either standardized trademarks (XEROX) or acronyms (XC). No words in the Basic English vocabulary begin with X, but it occurs in words beginning with other letters. It is often found in a word with an E before it. X is the third most rarely used letter in the English language.^{[citation needed]}
• French: at the ends of words, silent (or [z] in liaison if the next word starts with a vowel). This usage arose as a handwriting alteration of final -us. Two exceptions are pronounced [s]: six and dix. It is pronounced [z] in sixième and dixième.
• In Italian, X is either pronounced [ks], as in extra, when it is followed by a consonant, or [ɡz], as in the words uxorio and xilofono, when it is followed by a vowel. In several northern regional languages, notably Venetian, it represents the voiced sibilant [z]. It is also used, mainly amongst the young, as a short written form for "per", meaning "for": for example, "x sempre" ("forever"). This because in Italian the multiplication sign (similar to x) is called "per". However, X is only found in loanwords, as it is not part of the standard Italian alphabet; in most words that have become of common use, it has been replaced by the CS sequence.
• In Norwegian, X is generally pronounced [ks], but since the nineteenth century there has been a tendency to spell it out as ks whenever possible; it may still be retained in names of people, though it is fairly rare, and occurs mostly in foreign words and SMS language. Usage in Swedish, Danish, German and Finnish is similar.
• Spanish: 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, the hard [x] sound is spelled with a j, or with a g before e and i, though x is still retained for some names (notably México, which alternates with Méjico). Now, X represents the sound [s] (word-initially), or the consonant cluster [ks] (e.g. oxígeno, examen). Even more rarely, the x can be pronounced [ʃ] as in Old Spanish in some proper nouns such as Raxel (a variant of Rachel) and Uxmal.
• In Galician (a language related to Portuguese and spoken in Northwestern Spain), and Leonese, used in Spain, x is pronounced [ʃ] in most cases. In learned words, such as 'taxativo' (taxing), the x is pronounced [ks]. However, Galician speakers tend to pronounce it [s], especially when it appears in implosive position, 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 sounds; the most common is [ʃ], as in 'xícara' (cup). The other sounds are: [ks] as in 'fênix/fénix' (phoenix), [s], as in 'próximo' (close/next), and (the rarest) [z], as in 'exagerado' (exaggerate).
• 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 Uyghur (Latin script), x represents the sound [χ].
• 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).

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] in e.g. Azerbaijani, Kurdish, Lojban, Tatar, Uzbek, and Uyghur (Latin script).
• Esperanto: The x-convention replaces ĉ, ĝ, ĥ, ĵ, ŝ, and ŭ with cx, gx, hx, jx, sx, and ux.
• In Hanyu Pinyin, a transcription system for Mandarin Chinese, the letter x represents the voiceless alveolo-palatal fricative /ɕ/. This sound somewhat resembles [ʃ].
• In Hindi, x represents the sound [kʃ] in alternate spellings of words containing क्ष, especially names such as Laxmi or Madhuri Dixit.
• In Nahuatl, x represents [ʃ].
• Nguni languages: x represents the alveolar lateral click [ǁ].
• In Pashto, x represents [dz].
• In Pirahã, x symbolizes the glottal stop [ʔ].
• An illustrating example of x as a "leftover" letter is differing usage in three different East Cushitic languages:
  • Afar language: voiced alveolar implosive [ɗ]
  • Oromo language: alveolar ejective [tʼ]
  • Somali language: voiceless pharyngeal fricative [ħ]

In Southeast Asia and China

• 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 romanization of Lao consonants, X may represent the same sound, e.g. in Lan Xang, where the parallel Thai alphabetic character for the same word is pronounced chang.
• In romanization of Mandarin Chinese, "X" is used extensively, e.g., Xi (surname) Mandarin pronunciation: [ɕi].
• Pinyin, the official system to transcribe Chinese characters into Latin script in China, Malaysia, Singapore and Taiwan, similarly uses X/x.

Related letters and other similar characters

• Χ χ : Greek letter Chi
• א : Hebrew letter Aleph
• Х х : Cyrillic letter Kha
• ᚷ : Gyfu, a letter in the Anglo-Saxon futhorc runic alphabet used in pre-Norman Britain.
• 乂 : a Chinese character, pronounced [i] (high falling tone), "yì" in pinyin
• ㄨ : a letter representing [u] or [w] in Mandarin Phonetic Symbols
• メ : Me, a Japanese katakana character
• × : Multiplication sign
• Ⓧ : a symbol used in Japan for resale price maintenance

Computing codes

character	X	x
Unicode name	LATIN CAPITAL LETTER X	LATIN SMALL LETTER X
character encoding	decimal	hex	decimal	hex
Unicode	88	0058	120	0078
UTF-8	88	58	120	78
Numeric character reference	X	X	x	x
EBCDIC family	231	E7	167	A7
ASCII 1	88	58	120	78

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

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

Other representations

NATO phonetic	Morse code
X-ray	–··–

Signal flag	Flag semaphore	Braille

See also

• XX
• XXX
• XXXX
• X mark
• commonly used as a prefix term in nouns about X Window & Unix

External links

• Media related to X at Wikimedia Commons
• The Wiktionary entry for X
• The Wiktionary entry for x

The ISO basic Latin alphabet
Aa	Bb	Cc	Dd	Ee	Ff	Gg	Hh	Ii	Jj	Kk	Ll	Mm	Nn	Oo	Pp	Qq	Rr	Ss	Tt	Uu	Vv	Ww	Xx	Yy	Zz
Letter X with diacritics
Ẍẍ	Ẋẋ	ᶍ
Related
History Palaeography Derivations Diacritics Punctuation Numerals Unicode List of letters ISO/IEC 646