The people of Cornwall and Wales, seven or eight hundred years ago used to frighten their children with tales of fearful hobgoblins or specters.
We don’t know what those ancient tales were nor how they described those imaginary creatures which became very real beings to the children. The Welsh term for specter is bug. The English in telling about the Welsh specter called it bug, for the original meaning of that word was “specter” or “ghost.”
The word hasn’t been used in that sense for several centuries, however, except in bugbear and bugaboo, but became another term for “beetle,” some varieties of which resemble a hideous specter.
In bugbear, the thought may have been a ghostly bear of very frightening appearance, but the concluding syllables of bugaboo were apparently meaningless, possibly resulting from nothing more than alliteration.
Bogy, or bogey, which now has the original meaning of bug, was probably a dialectal form of the older word.