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

Uses

Apart from being a part of the Latin alphabet, "X" the letter is a Roman numeral representing 10. In mathematics it is commonly used as the name for an independent variable. As a result it is often used to represent unknowns in other circumstances (e.g. Person X, Place X, etc.(see Malcolm X)).

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 “šei,” which was written xei, and was soon habitually abbreviated to x. (The Spanishpronunciation of “x” has changed since). This started the habit of using letters to represent quantities in algebra. In mathematics, an “italicized x” () is often used to avoid potential confusion with the multiplication symbol.

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 may also be used to signify the multiplication operation when a more appropriate glyph is unavailable. 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 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/; omegawas 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 as Tessel. This 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). It can also represent the sounds [ɡʒ] or [kʃ], for example, in the words luxury and sexual, respectively. 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.
• 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 always pronounced [ks], as in the words uxorio, extra, xilofono. It is also used, mainly amongst younger generations as a short form for "per" meaning "for", for example, x sempre (forever). This because in Italian the multiplication sign (similar to x) is called "per". An exception occurs in the archaic spelling of the Venetian dialect, where it represents [z], example: Venexia.
• 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 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 rarer, the x can be pronounced [ʃ] like in Old Spanish in some proper nouns such as Raxel (a variant of Rachel) and Uxmal.
• Galician and Leonese language: In Galician (a language related to Portuguese and spoken in Northwestern Spain), and Leonese, in Spain, x is pronounced [ʃ] in most cases. In learned words, such as 'taxativo' (taxative), the x is pronounced [ks]. However, Galician speakers tend to pronounce it as [s], especially when it appears in implosive position, such as in 'externo' (extern).
• In Catalan, x can have 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 [ʒ] before voiced consonants; 'caixmir'. There is also in Catalan the digraph tx, pronounced [tʃ].
• In Portuguese, x can have four sounds: the most common is [ʃ], as in 'xícara' (cup). The other sounds are: [ks] as in 'fênix/fénix' (phoenix) and [s], as in 'próximo' (close/next). The rarest is [z], as in 'exagerado' (exaggerate).
• Venetian:it represented the voiced alveolar fricative [z] much like in Portuguese 'exagerado', English 'xylophone' or in the French liaison. Examples from medieval texts include 'raxon' (reason), 'prexon' (prison), 'dexerto' (desert), 'chaxa/caxa' (home, It. "casa"). Nowadays, the most known word is 'xe' (is/are).
• 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 has its IPA value [x] in e.g. Kurdish, Azerbaijani, Uzbek, Tatar and Lojban.
• 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, it may represent 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: represents the alveolar lateral click [ǁ].
• In Pashto, x represents [dz].
• In Pirahã, x symbolizes the glottal stop [ʔ].
• In Vietnamese, x is pronounced [s]
• 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 Japan, Ⓧ is a symbol used for resale price maintenance.