A menacing, ghost-like monster in children's stories.
Near-synonyms: bogeyperson, bogeywoman
(figuratively, by extension) Any make-believe threat, especially one used to intimidate or distract; a real threat greatly exaggerated for those purposes.
Near-synonyms: bug-a-boo, bugaboo, chimera
The bogeyman of a Halloween-candy poisoner behind every door has animated occasional moral panics against trick-or-treating.