Necromancer is a fancy word for a magician. A necromancer might mix up a love potion or cast a spell on your mortal enemy.
You can use the noun necromancer when you talk about a sorcerer of any kind, but it most often refers to someone who can communicate with the dead. Your cousin who has good luck contacting spirits through her Ouija board might be an aspiring necromancer. For many people, the word has a dark, scary connotation, or a connection with black magic. The Greek word at the root of necromancer is nekromanteia, which joins nekros , "dead body," with manteia, "divination."