bogeyman vs bug-a-boo

bogeyman

noun
  • Any make-believe threat, especially one used to intimidate or distract. 

  • A menacing, ghost-like monster in children's stories. 

bug-a-boo

noun
  • Any imagined fear or threat, or a fear presumed larger than it really is. 

  • A mythical, nocturnal creature; a hobgoblin. 

How often have the words bogeyman and bug-a-boo occurred in a corpus of books? (source: Google Ngram Viewer )