In French (with a few exceptions), Italian, Romanian, and modern Spanish, ⟨x⟩ was replaced by other letters.

Similarly, the sequence ⟨xu⟩ can be pronounced with /kʃ/ (e.g. flexure, sexual) or /ɡʒ/ (in luxury and its derivatives).

Many of the words that start with ⟨x⟩ are of Greek origin, standardized trademarks (Xerox), or acronyms (XC).

In abbreviations, it can represent "trans-" (e.g. XMIT for transmit, XFER for transfer), "cross-" (e.g. X-ing for crossing, XREF for cross-reference), "Christ-" (e.g. Xmas for Christmas, Xian for Christian), the "crys-" in crystal (XTAL), "by" (SXSW for South by Southwest), or various words starting with "ex-" (e.g. XL for extra large, XOR for exclusive-or, or the extinction symbol).

In the Romance languages, as a result of assorted phonetic changes, ⟨x⟩ has other pronunciations: In languages which adopted the Latin alphabet later, ⟨x⟩ is used for various sounds, in some cases inspired by Latin or its descendants, but in others for unrelated consonants.