neenja
A higher classification of ninja, shinobi, or any other synonym for an assassin from early Japan. Neenjas are sneakier, better, smarter, deadlier, and harder to notice than normal ninjas. Just because you doubt that he is a ninja, there is still a chance that he is a neenja, which is more powerful. Neenjas have many traits that are commonly associated with ninjas, but may  not neccesarily do everything like a ninja. For instance, neenjas do not always have an arseanal of katanas, shurikan, and other weapons, they are all optional. A neenja can use his bare hands to murder an opponent. Neenjas' weapons of choice, however, are daggers and garrotes.
A  true neenja has a long list of kills, but the list is never recorded.