"something to frighten a child, fancied object of terror," 1843, earlier buggybow (1740), probably an alteration of bugbear (also see bug (n.)), but connected by Chapman ["Dictionary of American Slang"] with Bugibu, demon in the Old French poem "Aliscans" from 1141, which is perhaps of Celtic origin (compare Cornish bucca-boo, from bucca "bogle, goblin").
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