The definition of the word "mountweazel" is the following: "any invented word or name inserted in a reference work by a publisher for the purpose of detecting plagiarism". In her funny and informative podcast on linguistic facts, English writer Helen Zaltzman from The Allusionist, explores the existence of fake entries in dictionaries and encyclopedias.
In the 1975 version of the New Columbia Encyclopedia had this fake entry: Lillian Virginia Mountweazel. Apparently, Mountwezel was a fountain designer and photographer, who died in an explosion while on an assignment for the Combustibles magazine. This is not the only fake entry that reference books inserted among real entries. Fake items, also called "ghost words" and "nihil articles", are a widespread method used by dictionaries and encyclopedias to detect if other publishers copy their work. Considering the nature of such activities, copyright infringement is hard to detect in reference works. For this reason, inserting a false definition in a dictionary is still the only way to detect copycats.
What is even more interesting is that encyclopedias and dictionaries are not alone. Cartographers also use fake locations to protect their work. The practice is called phantom settlements, trap streets or paper towns. What this means is that when you are using the maps application on your smartphone and cannot find where you have to go, perhaps you might be searching for a place that does not really exist. So, don't trust Google Maps too much!