X (ĕks). X, the twenty-fourth letter of the
English alphabet, has three sounds; a compound nonvocal sound (that of
ks), as in wax; a compound vocal sound (that of
gz), as in example; and, at the beginning of a word, a
simple vocal sound (that of z), as in xanthic. See
Guide to Pronunciation, §§ 217, 270, 271.
The form and value of X are from the Latin X, which is from the
Greek Χ, which in some Greek alphabets had the value of ks,
though in the one now in common use it represents an aspirated sound
of k.