Common words:
* X-ray
* Xerox (a brand name, but often used as a verb)
Less common words:
* Xenon (a chemical element)
* Xenophobia (fear of foreigners)
* Xylophone (a musical instrument)
* Xylography (the art of wood engraving)
Words derived from proper nouns:
* Xanthippe (a woman known for her temper, from a Greek name)
* Xavier (a male name, often associated with Saint Francis Xavier)
Technical terms:
* X chromosome (a type of chromosome)
* X-axis (a horizontal axis in a coordinate system)
Other:
* X marks the spot (a common phrase)
There are other words that begin with X, but they are mostly technical or specialized terms, foreign words, or abbreviations.
Therefore, there are a limited number of words that begin with X in the English language, compared to other letters.