The Collaborative International Dictionary of English v.0.48:

flugelhorn \flugelhorn\, flugelhorn \fl["u]gelhorn\[from German
   fl["u]gelhorn.] n.
   A brass wind instrument resembling a cornet but with a wider
   bore, and having three valves.

   Syn: fluegelhorn.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

flugelhorn
    n 1: a brass instrument resembling a cornet but with a wider
         bore [syn: flugelhorn, fluegelhorn]