With its long, ambiguous history and multiple phonemes, the letter X is quite a dark horse. It can mean Christ, like the X in Xmas, stand for a chromosome, and even show up in friendly and amorous correspondence (XOXO).

But, how did X end up in the alphabet to begin with?

The origin of X

Since its inception, the letter X has struggled to establish its own identity, so it may be no coincidence that X is commonly used to represent the unknown in both language and mathematics. But, how was it created?X is derived from the Phoenician letter samekh, meaning “fish.” Originally used by the Phoenicians to represent the /s/ consonant (denoting a hard S sound), the Greeks borrowed the samekh around 900 BC and named it Chi.

The ancient Greeks utilized their newly acquired phonological element to simplify the digraph (“a pair of letters representing a single speech sound”) /ks/, which is used most prominently throughout the western regions of Greece.

The Romans later adopted the X sound from the Chalcidian alphabet, a non-Ionic Greek alphabet, and borrowed the Chi symbol, consisting of two diagonally crossed strokes, from the Greek alphabet to denote the letter X as well as to identify the Roman numeral X or “10.”

So to sum up: The Romans took the /x/ sound from one alphabet (Chalcidian) and combined it with the Chi symbol from another alphabet (Greek) and thus X was born.

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How to say X

Like many letters in the English language, such as C and J, X is a bit of a phonetic chameleon. For instance, X is used to establish the /ks/ sound, as in wax and fox—referred to as a “voiceless velar fricative,” in case you were really wondering. This articulation is made by placing the back of the tongue at the soft palate.

The same rule applies for X’s /gz/ sound, as in auxiliary and exhaust. X can also take on the /z/ sound as in xylophone and Xanadu, the hard /k/ sound as in excite, and /kzh/ as in luxury. The X can also be silent as in Sioux (Falls), and the French loan-word faux.