The origins of the town name of Royal Tunbridge Wells are logical, as The Concise Oxford Dictionary Of English Place points out, but they are a little confused by the different spelling to nearby Tonbridge. The book notes that “named from Tonbridge, the medicinal springs are said to have been discovered in the times of James I”. Although disputed by some historians, Tonbridge is named after “Tunna’s Bridge” according to the book and the place name spellings have switched between Tonbridge and Tunbridge over the centuries.
The reason to have different spellings seems to have been more recent, likely from the early part of the twentieth century, a deliberate attempt to show that the two settlements were very different places. The Royal bit of the name dates from 1909, when the honour was granted by King Edward VII to mark the popularity of the town with the Royal Family.