Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Beelzĕbŭb, indecl., or Beelzĕbŭl, ūlis, m., = Βεελζεβούβ or Βεελζεβούλ, Heb. [??] or [??]; in eccl. Lat. Beelzebub, the chief of evil spirits, Vulg. Luc. 11, 15; Tert. adv. Marc. 4, 26; Prud. στεφ. 2, 267.