The Collaborative International Dictionary of English v.0.48:

Bogle \Bo"gle\, n. [Scot. and North Eng. bogle, bogill, bugill,
   specter; as a verb, to terrify, fr. W. bwgwl threatening,
   fear, bwg, bwgan, specter, hobgoblin. Cf. Bug.]
   A goblin; a specter; a frightful phantom; a bogy; a bugbear.
   [Written also boggle.]
   [1913 Webster]