Someone who looks spookily like you, but isn't a twin, is a doppelganger. Originally, this was a type of ghost.

The word doppelganger is German and literally means double walker — as in a ghost or shadow of yourself. An easy way to remember it is that doppelganger sounds like double, as in "That movie star is my double. We look so much alike." These days, most people don't refer to the ghost meaning when talking about doppelgangers: they just mean someone who looks a lot like you or could be your twin. Still, that is pretty spooky.

Definitions of doppelganger

n a ghostly double of a living person that haunts its living counterpart

Type of:
legendary creature
a monster that is unverifiable but popularly accepted as possibly factual