Bugbear
A bugbear is a legendary creature or type of hobgoblin comparable to the boogeyman, and other creatures of folklore, all of which were historically used in some cultures to frighten disobedient children.
Etymology
Its name is derived from the Middle English word "bugge", or perhaps the Old Welsh word bwg, or Old Scots bogill, and cognates most probably English "bogeyman" and "bugaboo".In medieval England, the bugbear was depicted as a creepy bear that lurked in the woods to scare children. It was described in this manner in The Buggbears, an adaptation, with additions, from Antonio Francesco Grazzini’s La Spiritata.
In a modern context, the term bugbear may also mean pet peeve.