Definitions

1. noun

A double-u, the 22nd letter of the modern English alphabet.

“The word ‘double-u’ is often used to describe the letter ‘xw’, but more commonly it refers to ‘xw’ is not a word, I assumed you meant ‘double-u’ as in the letter ‘w’. However, if we were to describe ‘xw’ in a similar manner, it could be used in a sentence such as: The alphabet contains 26 letters, with the letter ‘xw’ not being one of them.”