# Xi (letter)

**Xi** (Ξ, ξ; Greek ξι) is the fourteenth letter of the [Greek alphabet](https://www.edgepedia.org/greek-alphabet), representing the voiceless consonant cluster /ks/ in both classical [Ancient Greek](https://www.edgepedia.org/ancient-greek) and [Modern Greek](https://www.edgepedia.org/modern-greek).<sup>[1](https://graphsearch.epfl.ch/en/concept/166742)</sup> It descends from the Phoenician letter samek and has no descendant in the Latin alphabet, so it never reached English as a letter, although the word "xi" entered English as a name for the letter in the early fifteenth century.<sup>[2](https://www.etymonline.com/word/xi)</sup>

| Key fact | Detail |
|---|---|
| Position and forms | Fourteenth letter of the Greek alphabet; uppercase Ξ, lowercase ξ, name spelled ξι<sup>[1](https://graphsearch.epfl.ch/en/concept/166742)</sup> |
| Sound | The consonant cluster /ks/, the same value in Ancient and Modern Greek<sup>[1](https://graphsearch.epfl.ch/en/concept/166742)</sup> |
| Phoenician ancestor | Samek (𐤎), which followed the symbol for nun in the Phoenician order<sup>[3](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Alphabet)</sup> |
| Early variant spellings | In some early Greek alphabets the cluster was written analytically as ΚΣ (or ΚΜ) rather than with the single sign Ξ<sup>[4](https://en.wikisource.org/wiki/Page%3AEncyclop%C3%A6dia_Britannica%2C_Ninth_Edition%2C_v._1.djvu/648)</sup> |
| Old Italic descendant | Esh (𐌎), the Old Italic letter corresponding to Greek xi<sup>[5](https://www.kaese.name/Typography/Alphabet_evolution.html)</sup> |
| Fate in Latin | Xi dropped out of use in Latin and so never entered the English alphabet<sup>[6](https://www.drshirley.org/greek/textbook02/chapter01-alphabet.pdf)</sup> |

## Sound and name

In both classical Ancient Greek and Modern Greek, Ξ stands for the cluster /ks/, a sound English writers usually render with the letter x.<sup>[1](https://graphsearch.epfl.ch/en/concept/166742)</sup> Koine-era teaching sources give its pronunciation as "x as in taxi".<sup>[6](https://www.drshirley.org/greek/textbook02/chapter01-alphabet.pdf)</sup> The English name of the letter has two accepted pronunciations, /ˈzī/ and /ˈksī/, and [Merriam-Webster](https://www.edgepedia.org/merriam-webster) derives the word from Greek *xei*; the dictionary dates the word's first known use in English to the fifteenth century.<sup>[7](https://www.merriam-webster.com/dictionary/xi)</sup> Etymonline likewise records "xi" as the name of the fourteenth Greek letter in English by the early fifteenth century.<sup>[2](https://www.etymonline.com/word/xi)</sup>

In the Greek alphabetical order, xi sits between nu and omicron, a position it inherits from the Phoenician sequence. Learners of Greek often notice that zeta and xi, which look similar with their horizontal bars, both seem misplaced relative to the [English alphabet](https://www.edgepedia.org/english-alphabet); the [Open University](https://www.edgepedia.org/open-university)'s Greek course points to the jingle "zeta-eta-theta" as a memory aid for that stretch of the order.<sup>[8](https://www.open.edu/openlearn/mod/oucontent/view.php?id=157789&section=_unit2.2.7)</sup>

## Origin from Phoenician samek

The Greek alphabet was adapted from the [Phoenician alphabet](https://www.edgepedia.org/phoenician-alphabet), with the order and names of the letters derived from Phoenician, and it has been in continuous use since about 750 BC.<sup>[9](https://www.omniglot.com/writing/greek.htm)</sup> Xi corresponds to Phoenician samek (𐤎). The 1911 *Encyclopædia Britannica* account of the Greek treatment of the Phoenician sibilants places samek, an ordinary s-sound, immediately after the symbol for n in the Phoenician order, and notes that the history of the symbol ξ belongs to the sibilant question alongside zeta.<sup>[3](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Alphabet)</sup>

A comparative typography chart of alphabet evolution traces the line further back and forward: Egyptian hieroglyph R011 (𓊽), Phoenician semk (𐤎), Greek capital xi (Ξ, Unicode U+039E), and the Old Italic letter esh (𐌎).<sup>[5](https://www.kaese.name/Typography/Alphabet_evolution.html)</sup> The hieroglyphic step in such charts is a reconstruction rather than an established fact, and specialist accounts generally begin the secure chain with the Phoenician letter.<sup>[3](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Alphabet)</sup>

## Regional variants in the early Greek alphabets

Before the Ionic alphabet became standard, several local Greek alphabets handled the /ks/ cluster differently. The ninth-edition *Britannica* records that in some alphabets ξ was written not as a single sign but as the two-letter sequence ΚΣ (or ΚΜ).<sup>[4](https://en.wikisource.org/wiki/Page%3AEncyclop%C3%A6dia_Britannica%2C_Ninth_Edition%2C_v._1.djvu/648)</sup> The *Oxford Classical Dictionary* notes that certain Greek states found no use for Ξ, which it describes as properly perhaps a more complicated sibilant than the simple x of later usage, and that some states wrote the sibilant with san (Μ) instead of sigma.<sup>[10](https://academic.oup.com/edited-volume/61673/chapter-abstract/548074837)</sup>

**Red and blue alphabets.** Scholars group the early Greek local alphabets by how they assigned the supplemental letters. In the group conventionally called the red alphabets, the letter Χ was used to denote the sequence /ks/, the value that the classical (blue) alphabet gave to Ξ.<sup>[11](https://classics.brown.edu/sites/default/files/BCJ/BCJ-Volume-33.pdf)</sup> A study of the Euboean alphabet, which formed the basis of the Etruscan script, describes its form of xi as a "dark blue" xi that in time became a dead letter in the alphabets of Boeotia and Euboea and was eventually dropped in favor of red xi (X), which was added at the end of the alphabet.<sup>[12](https://doi.org/10.4000/1214v)</sup> This regional variation is the background to the Latin letter X: the Western Greek alphabet used Χ for the x-sound and placed it at the end, and the [Latin alphabet](https://www.edgepedia.org/latin-alphabet) inherited both the form and the position.<sup>[13](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/O)</sup>

## Later history

When the Romans built their alphabet on Etruscan and Western Greek models, xi did not survive; a Greek-teaching source states that "Xi dropped out of use in Latin, and so never made it into English".<sup>[6](https://www.drshirley.org/greek/textbook02/chapter01-alphabet.pdf)</sup> The letter did pass into other scripts derived from Greek: Church Slavonic includes a letter Xi modeled on the Greek one, and typographic studies compare the Slavonic and Greek forms directly.<sup>[14](https://www.tug.org/TUGboat/Articles/tb17-2/tb51omeg.pdf)</sup> In the modern era the letter is encoded in Unicode at U+039E (Ξ) and U+03BE (ξ) in the Greek and Coptic block.<sup>[5](https://www.kaese.name/Typography/Alphabet_evolution.html)</sup>

## References

1. [Xi (letter), EPFL Graph Search](https://graphsearch.epfl.ch/en/concept/166742)
2. ["xi", Online Etymology Dictionary](https://www.etymonline.com/word/xi)
3. ["Alphabet", Encyclopædia Britannica, 11th edition (1911), Wikisource](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Alphabet)
4. [Encyclopædia Britannica, Ninth Edition, v. 1, page 648, Wikisource](https://en.wikisource.org/wiki/Page%3AEncyclop%C3%A6dia_Britannica%2C_Ninth_Edition%2C_v._1.djvu/648)
5. [Evolution of the alphabet, kaese.name typography reference](https://www.kaese.name/Typography/Alphabet_evolution.html)
6. [Shirley J. Rollinson, "The Greek Alphabet", chapter 1 (2014)](https://www.drshirley.org/greek/textbook02/chapter01-alphabet.pdf)
7. ["xi", Merriam-Webster Dictionary](https://www.merriam-webster.com/dictionary/xi)
8. [Getting started on ancient Greek: 8, The Open University, OpenLearn](https://www.open.edu/openlearn/mod/oucontent/view.php?id=157789&section=_unit2.2.7)
9. [Greek language and alphabets, Omniglot](https://www.omniglot.com/writing/greek.htm)
10. ["Alphabet, Greek", Oxford Classical Dictionary, Oxford Academic](https://academic.oup.com/edited-volume/61673/chapter-abstract/548074837)
11. [Linguistic Variation 17, Brown Classical Journal Volume 33](https://classics.brown.edu/sites/default/files/BCJ/BCJ-Volume-33.pdf)
12. [Contacts linguistiques en Grèce ancienne, MOM Éditions](https://doi.org/10.4000/1214v)
13. ["O", Encyclopædia Britannica, 11th edition (1911), Wikisource](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/O)
14. [Church Slavonic Typography in the Unicode Standard, Unicode Technical Note 41](https://www.tug.org/TUGboat/Articles/tb17-2/tb51omeg.pdf)

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*Topic: Encyclopedia › Society and history › Languages and linguistics › Writing and notation systems › Mediterranean, Italic, and undeciphered ancient scripts*

*Initially written Sep 17, 2026 · Reviewed: Oct 25, 2026 · Edited: Oct 15, 2026; Oct 25, 2026 · Last review: Oct 25, 2026*

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