How Are “William” and “Guillermo” Related?

Justin in Dallas, Texas, is curious about the origin of the name William, and why the Spanish version is Guillermo. Its popularity goes back to the days of William the Conqueror. Modern languages have several versions of this name, such as German Wilhelm and Dutch Willem. For a good explanation of the phonetic changes that led to these different versions, check out Trask’s Historical Linguistics by R. L. Trask, revised and edited by Robert McColl Miller. (Bookshop|Amazon) This is part of a complete episode.