Pokemon: Gastly, Haunter & Gengar

Name origin:
Gastly: may be a combination of gas and ghastly (like a ghost; dreadfully frightening).

Haunter: is derived from haunt, as ghosts are known to do. It could also be a corruption of "hunter".

Gengar: and Gangar are possibly a shortening of doppelgänger, a double of a person, which is fitting for a Pokémon with a habit of pretending to be a person's shadow. The kanji 幻 maboroshi can also be read as gen and is used in words meaning phantom or illusion. There is also a striking pronunciation similarity to the Danish word genganger, a term for ghosts found in Scandinavian folklore.