Misnomer, and it means that something is misnamed. For example if I called your cat "doggy" it would be a misnomer becuase dog is the incorrect name for a cat.
Misnomer, indeed. I was always wondering what guilder meant. Completely forgot about the currency. You should remember that masons are also a pseudo-mystical illuminati-type group from the 1800's who were supposed to control everything. So there's a different meaning there, too... and a cooler one. I could totally see Biggles and Coolant wearing black hoods, chanting, and sacrificing peons.