Over the past 400 years, the forms of the language used in the Americas—especially in the United States—and that used in the United Kingdom have diverged in a few minor ways, leading to the versions now often referred to as American English and British English. Differences between the two include pronunciation, grammar, vocabulary (lexis), spelling, punctuation, idioms, and formatting of dates and numbers. However, the differences in written and most spoken grammar structure tend to be much less than in other aspects of the language in terms of mutual intelligibility. A few words have completely different meanings in the two versions or are even unknown or not used in one of the versions. One particular contribution towards formalising these differences came from Noah Webster, who wrote the first American dictionary (published 1828) with the intention of showing that people in the United States spoke a different dialect from those spoken in the UK, much like a regional accent.