Can you name any common word with a double U?

The double 'U' is one of the rarest vowel combinations in the English language. While we are perfectly comfortable with double 'E' (as in 'see') and double 'O' (as in 'book' or 'moon'), the 'UU' pairing almost never appears in native English words. The most famous example, and the one most people can name, is 'vacuum'. Its unusual spelling is a direct clue to its origin.

Many of these words, including 'continuum', 'residuum', and 'vacuum' itself, are direct imports from Latin. In Latin, the "-uum" ending was common for certain types of nouns, and when these words were adopted into English, they kept their original spelling. Another Latin-derived example is 'duumvirate', a term for a government led by two officials, which combines the Latin words for "two" (duo) and "men" (viri).

Not all instances of 'UU' come from ancient Rome, however. The word 'muumuu', a term for a loose-fitting dress, was borrowed from the Hawaiian language in the 19th century. Ultimately, the reason these words stand out is that they are loanwords. They preserve the spelling of their original language rather than conforming to typical English phonetic patterns, making them fascinating exceptions to the rule.