The bucca is a form of a Cornish spirit or hobgoblin from south-west of England. Buccas tend to keep to themselves and need to be respected properly since they are the spirits of the land and sea. Fishermen would always leave a fish for a bucca after they had a catch and at harvest where it was essential to leave a piece of bread and some beer when the harvester had their lunch. From such respects, the bucca rapidly descended in people’s options to a mere bucca-boo from this we get the term bugga-boo or bogeyman.
John and Caitlin Matthews, The Element Encyclopaedia of Magical Creatures, 2013, Bucca, p 76