Nincompoop is not a meaningless word as some people maintain. Try calling your boss a nincompoop and see what happens. More correctly, it is ‘nonsense word’ that has meant, fool, blockhead, idiot, etc, since the 17th century. No less a person than Samuel Johnson in 1775 tried to make a case that it was a corruption of the Latin non compos mentis, which was widely used by doctors and lawyers in everyday speech and often shortened to non compos. Johnson argued that to the uneducated masses, non compos could well sound like nincompoop. Most etymologists, however, remain unconvinced and simply classify it as a nonsense word of unknown origin. There is no denying, however, that it sounds very much like what it purports to describe.