Source : Webster's Revised Unabridged Dictionary (1913)

Beelzebub \Be*el"ze*bub\, n.
   The title of a heathen deity to whom the Jews ascribed the
   sovereignty of the evil spirits; hence, the Devil or a devil.
   See {Baal}.

Source : WordNet®

Beelzebub
     n : (Judeo-Christian and Islamic religions) chief spirit of evil
         and adversary of God; tempter of mankind; master of Hell
         [syn: {Satan}, {Old Nick}, {Devil}, {the Devil}, {Lucifer},
          {the Tempter}, {Prince of Darkness}]