The letters of the alphabet that are used least frequently in the English language are Q, J, Z and X. Each of these letters is used in less than one percent of English vocabulary. Of these, X is the least common letter at the beginning of words.
By contrast, the letter E is the most frequently used in the English vocabulary. It appears in more than 11 percent of words. The letters R, N, T and S are not too far behind, with S being the most common letter at the start of words.
Of the vowels, which are all used fairly frequently, the letter U occurs the least often.