Definition and background:
An early 19th century ophicleide.A 19th century valved tuba.A low reed stop for the pedals of 19th century Walcker pipe organs.
A bass tuba, generally in E-flat with three or four valves
For more information on the music term "Bombardon" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary