One who gets pleasure (often sexual) from the suffering of others. It is a common myth that sadists like masochists, however the true sadist can get no pleasure from the pain he causes the masochist because the masochist is enjoying it.
*Masochist sees a sadist (identified by the whip and handcuffs in his back pocket) and sees an opportunity for a beautiful relationship*
One who has a sadistic personality disorder which is characterized by deriving satisfaction from the physical or psychological suffering of another person. A person of this type is controlling, likes to humiliate a person in public, disciplines brutally when in a position of power, and likes to intimidate people.
The sadistic parent excessively whipped his child because they forgot to take out the garbage.