Note: Here's an interesting "Word History" from Dictionary.com:
Alphabet books for children frequently feature the word xylophone because it is one of the few words beginning with x that a child (or most adults, for that matter) would know. The majority of English words beginning with x, including many obscure scientific terms, are of Greek origin, the x, pronounced (z), representing the Greek letter xi. In the case of xylophone, xylo- is a form meaning "wood," derived from Greek xulon, "wood," and -phone represents Greek phōnē, "voice, sound," the same element found in words such as telephone, microphone, and megaphone. Our famous x word is first recorded in the April 7, 1866, edition of the Athenaeum: "A prodigy . . . who does wonderful things with little drumsticks on a machine of wooden keys, called the 'xylophone.'"