The Collaborative International Dictionary of English v.0.48:

Bugbear \Bug"bear`\, n.
   Same as Bugaboo. -- a. Causing needless fright. --Locke.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bugbear \Bug"bear`\, v. t.
   To alarm with idle phantoms.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bugaboo \Bug`a*boo"\, Bugbear \Bug"bear`\, n. [See Bug.]
   Something frightful, as a specter; anything imaginary that
   causes needless fright; something used to excite needless
   fear; also, something really dangerous, or an imaginary
   monster, used to frighten children, etc. "Bugaboos to fright
   ye." --Lloyd.
   [1913 Webster]

         But, to the world no bugbear is so great
         As want of figure and a small estate.    --Pope.
   [1913 Webster]

         The bugaboo of the liberals is the church pray. --S. B.
                                                  Griffin.
   [1913 Webster]

         The great bugaboo of the birds is the owl. --J.
                                                  Burroughs.
   [1913 Webster]

   2. a source of concern; as, the old bugaboo of inflation
      still bothers them.
      [WordNet 1.5]

   Syn: Hobgoblin; goblin; specter; ogre; scarecrow; bogeyman;
        boogeyman; booger.
        [1913 Webster]

WordNet (r) 3.0 (2006):

bugbear
    n 1: an imaginary monster used to frighten children [syn:
         bogeyman, bugbear, bugaboo, boogeyman, booger]
    2: an object of dread or apprehension; "Germany was always a
       bugbear for France"; "A foolish consistency is the hobgoblin
       of little minds"--Ralph Waldo Emerson [syn: bugbear,
       hobgoblin]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "bugbear":
   Dracula, Frankenstein, Mumbo Jumbo, Wolf-man, affliction, anathema,
   bane, bete noire, bogey, bogeyman, boggart, bogle, bogy, booger,
   boogerman, boogeyman, bug, bugaboo, bugger, burden, calamity,
   crushing burden, cry of wolf, curse, death, destruction,
   detestation, disease, dud, evil, false alarm, fee-faw-fum,
   frightener, ghost, ghoul, grievance, harm, hate, hobgoblin,
   holy terror, horror, incubus, infliction, monster, nemesis,
   nightmare, ogre, ogress, open wound, pest, pestilence, phantom,
   plague, revenant, running sore, scarebabe, scarecrow, scarer,
   scourge, specter, succubus, terror, thorn, torment, vampire,
   vexation, visitation, werewolf, woe