X the twenty-fourth letter of the English alphabet. Its
position and form are derived from the Latin alphabet,
which received them from the Western Greek alphabet.
The alphabet of the Western Greeks differed from the
Ionic, which is the Greek alphabet now in general use, by the
shape and position of X and of some other consonants. The
Ionic alphabet placed x (ξ) immediately after N and, in the
oldest records, in the form 
, from which the ordinary Greek
capital Ξ was developed. The position and shape of this
symbol show clearly that it was taken from the Semitic Samekh,
which on the Moabite stone appears as 𐤎. Why the Greeks
attached this value to the symbol is not clear; in Semitic the
symbol indicates the ordinary s. Still less clear is the origin
of the form X, which in the Ionic alphabet stands for χ (k
followed by a breath). In a very ancient alphabet on a small
vase found in 1882 at Formello near the ancient Veii in Etruria,
a symbol appears after N consisting of three horizontal and
three vertical lines, 
. From this it has been suggested that
both forms of the Greek x are derived, Ξ by removing the
vertical lines, X in its earliest form 
by removing the four
marginal lines. The Ionic symbol, however, corresponds closely
to the earliest Phoenician, so that this theory is not very plausible
for Ξ, and there are various other possibilities for the development
of X (see Alphabet). This symbol appears in the very
early Latin inscriptions found in the Roman Forum in 1899
as 
. In its usual value as ks it is superfluous. In the Ionic
alphabet it was useful, because there it represented a single
sound, which before the invention of the symbol had to be
represented by kh. In the alphabet in use officially at Athens
before 403 B.C. x was written by χσ (khs). In English there is
an interesting variation of pronunciation in many words according
to the position of the accent: if the accent precedes, x is
pronounced ks; if it follows, x is pronounced gz: compare éxit
(eksit) with exáct (egzact).
The symbol X was used both by the Romans and the Etruscans for the numeral 10. Which borrowed from the other is uncertain, but the Etruscans did not use X as part of their alphabet. X with a horizontal line over it was used for 10,000, and when a line on each side was added, |X|, for a million. (P. Gi.)