althorn

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several upright, valved brass wind instruments used especially in bands.

Century Dictionary and Cyclopedia

1. n. A musical instrument of the sax-horn class, often used in place of or with the French horn in military bands.

Wiktionary

1. n. music An alto or tenor saxhorn

GNU Webster's 1913

1. n. (Mus.) An instrument of the saxhorn family, used exclusively in military music, often replacing the French horn.