The letter X, sometimes known as x, is the twenty-fourth and last letter of the contemporary English alphabet as well as the ISO basic Latin alphabet. In English, it is known as “ex” (pronounced /ks/), plural exes.

‘X’ and ” were two variations of the same letter in Ancient Greek, first employed for /kh/ and subsequently, in western places like Arcadia, as a simplification of the digraph ” for /ks/. In the end, Classical Greek adopted more traditional eastern forms, and ” (Chi) stood for /kh/ (later /x/; palatalized to in Modern Greek before front vowels). The Etruscans, on the other hand, had adopted ” from western Greek, and it now stands for /ks/ in Etruscan and Latin.

The letter ” ” for /kh/ was added to the Greek alphabet after the Semitic letters, along with the letter phi ” for /ph/.

English

When it comes after a stressed vowel (e.g. ox), the voiceless consonant cluster /ks/ is used, and when it comes before a stressed vowel (e.g. z), the voiced consonant /z/ is used (e.g. exam). When it comes before a silent h and a stressed vowel, it’s pronounced /z/. (e.g. exhaust). It can be pronounced /k/ or / (e.g. sexual and luxurious) before I or u; they are the consequence of previous /ksj/ and /zj/. In words ending in -xion, it also creates the sound /k/. (typically used only in British-based spellings of the language; American spellings tend to use -ction). Except in foreign words like fake, when an x terminates a word, it is always /ks/ (e.g. fax) (see French, below).

There are just a handful words in English that begin with the letter x. (the fewest of any letter). When x begins a word, it is generally pronounced /z/ (e.g. xylophone, xenophobia, and xanthan); it can alternatively be pronounced /s/ (e.g. the obsolete Vietnamese monetary unit xu) or / in uncommon contemporary loanwords or foreign personal names (e.g. Chinese names starting with Xi like Xiaomi or Xinjiang). Many words beginning with the letter x are either standardized trademarks (Xerox) or acronyms (XC). It can stand for “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), “crys-” in crystal (XTAL), or various words beginning with “ex-” in abbreviations (e.g. XL for extra large, XOR for exclusive-or).

With a frequency of around 0.15 percent in words, X is the third least commonly used letter in English (after q and z).

An independent variable or unknown value is usually referred to as x in mathematics. René Descartes originated the contemporary custom of using x to indicate an unknown in La Géométrie (1637). X is frequently used to represent unknowns in various situations as a result of its use in algebra (e.g. X-rays, Generation X, The X-Files, and The Man from Planet X; see also Malcolm X).

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