Necromancer: one who practices divination by conjuring up the dead.
Necromancy is divination by raising the spirits of the dead. The word derives from the Greek nekrós "dead" and manteía "divination." It has a subsidiary meaning reflected in an alternative and archaic form of the word, nigromancy (a folk etymology using Latin niger, "black"), in which the magical force of "dark powers" is gained from or by acting upon corpses. A practitioner of necromancy is a necromancer.
"It is said that necromancy was another--older--name for mediums, spiritualists, and other people who could talk to ghosts. The meaning came from an ancient belief that if you could talk to the dead, they could predict the future because they could see everything--they'd know what your enemy was doing or where you could find buried treasure." (From The Awakening)
Necromancers are the link between the afterlife and the living world for all spirits. It is an ability they are born with, sometimes a gift, sometimes a curse, but ever-present in their lives.
They hear dead people - And dead people hear them. Certain herbs and relics can be (and frequently are) used to enhance or repel these phenomena, but necromancers are not spellcasters, and their power is inherant. Some incantations may be used as well, old sounding, and passed down from generation to generation, likely unique to one line of necromancer. The summoning of spirits is typically done graveside (or wherever the body rests), but a powerful necromancer may be able to call to a spirit from a distance, though exerting this show of power exhausts the necromancer for a few days, and renders them incapable of using their powers for a period no less than a week.
A necromancer who has been experimented on, Chloe Saunders, does not need herbs or relics or even a personal object of the deceased in order to summon a spirit. As well as, the ability to raise the dead with no complications or rituals; sometimes even on accident.
As natural conduits to the living world, an unlucky necromancer could be constantly haunted by restless spirits seeking favors or simply mischief. The minds of even the luckiest and most disciplined necromancers eventually crumble.