Bogeyman is a compound of bogey ('specter, goblin') + man; bogey is of obscure origin, related to dialectal bogle and boggart and possibly to Middle English bugge ('frightening specter'). The historical trail runs through bugge in Middle English. Morphologically, bogeyman is transparent: it is a compound of bogey ('specter, goblin') + man. Used as a noun, bogeyman now means "an imaginary evil spirit invoked to frighten children; a dreaded threat", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in related forms such as bogey, boggart, and bogle. That uncertainty is part of the entry: the safest account is the attested form and the limited comparisons preserved with it.