Wraith
A Scottish word, first used in English in 1513. A wraith is an apparition, vision, or double of another living person. Its appearance is commonly seen as an omen that the person being doubled is about to die.
– Pad of Definitions (1.01 Pilot (episode)), Official Website
According to hunter Martin Creaser, who draws the impression of a wraith shown at right, they "crack open skulls and feed on brain juice". They can pass as human, but their true form is revealed in a mirror. Wraiths can be killed by silver, and are burned when silver touches their skin.
5.11 Sam, Interrupted
In 5.11 Sam, Interrupted, the wraith is disguised as a nurse called Karla. She amplifies a person's imbalances to make the brain produce more chemicals like dopamine, which she likes to consume. She feeds on the brain through a thin pointed protrusion that emerges from her wrist, which she inserts into the brain. She is killed by Dean with a silver plated letter opener.
