Haunter n. : One who, or that which, haunts.

Example:
What level should I evolve Haunter into Gengar?

Taxonomy
Pokémon, Haunter Versus Kadabra, Pokédex, Generation, effectiveness, Game, Pokémon encyclopedia, victim, tongue, evolution, STAB, dimension, opponent, slip, steal, Bulbapedia, Atk, block walls.

Defination from the web:
Haunter is from another dimension because of this ability. ... In Fear Factor Phony, a Haunter was living in an abandoned mine with several other Ghost Pokémon. ...