In mathematics, 'x' is commonly used as the name for an independent variable or unknown value. Modern tradition of using 'x' to represent unknowns was started by René Descartes in his La geometrie (1637).
It may also be used to signify the multiplication operation when a more appropriate glyph is unavailable. In mathematics, an "italicized x" () is often used to avoid potential confusion with the multiplication symbol. Note that in any font the glyph of "x" is not exactly the same as one of the multiplication sign.
Other non-mathematical uses include:
- As a result of its use in algebra, 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.
- 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.
- X marks are used to indicate the concept of negation or incorrect, the opposite of a Tick (check mark). It is also used however as a substitute for the check mark (most notably on election Ballot papers)
- X is commonly used as a generic mark (selecting an item on a form, indicating a location on a map, etc.).
- The common custom of placing X's on envelopes, notes and at the bottom of letters to mean kisses dates back to the Middle Ages, when a Christian cross was drawn on documents or letters to mean sincerity, faith, and honesty.
- Usually in art or fashion, the use of X indicates a collaboration with two or more artists. The application extends to any other kinds of collaboration outside the art world.
- In cartoons, a dead character's eyes are often drawn as X's.
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.
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 in the name of the island of Texel, which is pronounced Tessel. This is because of 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'), but, sometimes, also, when adjacent with 'c' after it, [k] (e.g. 'excellent'), and 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 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).
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'. Three exceptions are pronounced [s]: six ("six"), dix ("ten") and Bruxelles. It is pronounced [z] in sixième and dixième.
- In Italian, 'x' is either pronounced [ks], as in extra, uxorio, xilofono, 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, 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 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 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 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 main sounds; the most common is [ʃ], as in 'xícara' (cup). The other sounds are: [ks] as in 'fênix/fénix' (phoenix); [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 [gz], coexisting with [z] and [ks] as acceptable pronunciations in exantema and in words with the Greek prefix 'hexa'.
- 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).
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, Pashto 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 Hindi, 'x' represents the sound [kʃ] in alternate spellings of words containing 'क्ष' (kshha), especially names such as Laxmi and Dixit. Less frequently,'x' is used to represent 'ख़' [xə] .
- In Nahuatl, 'x' represents [ʃ].
- 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 East Cushitic languages:
Usage in English
Usage in Southeast Asia and China
- 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, Mandarin 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]. This sound somewhat resembles [ʃ].
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
|Unicode name||LATIN CAPITAL LETTER X||LATIN SMALL LETTER X|
|Numeric character reference||X||X||x||x|
- 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 (0x or 0X) is used to denote hexadecimal literal values.
- "X", Oxford English Dictionary, 2nd edition (1989); Merriam-Webster's Third New International Dictionary of the English Language, Unabridged (1993); "ex", op. cit.
- Mička, Pavel. "Letter frequency (English)". Algoritmy.net.
- http://www.dizionario.rai.it Dizionario di ortografia e pronunzia
- Writing diacritic letters
- Media related to X at Wikimedia Commons
- The dictionary definition of X at Wiktionary
- The dictionary definition of x at Wiktionary
- "X". The American Cyclopædia. 1879.
Letter X with diacritics