I've checked the dictionary and it clearly states that 'sadist' is a noun and 'sadisctic' is an adjective. And if I were to say that, "She's sadistic" and "She's a sadist", to me both sentences refer to the same person in the same context. But someone told me that 'sadisctic' is an adjective for the person who becomes the victim of the act. So, is there such a thing?