The American Heritage® Dictionary of the English Language, 4th Edition
n. A keyed brass instrument of the bugle family with a baritone range that was the structural precursor of the bass saxophone and was replaced by the tuba in orchestras.
n. A keyed brass baritone bugle, now replaced by the tuba in orchestral music
the GNU version of the Collaborative International Dictionary of English
n. A large brass wind instrument, formerly used in the orchestra and in military bands, having a loud tone, deep pitch, and a compass of three octaves; -- now generally supplanted by bass and contrabass tubas. It developed from the older wooden instrument called the serpent.
The Century Dictionary and Cyclopedia
n. A metal musical wind-instrument, invented about 1790, having a large tube of conical bore, bent double, with a cupped mouthpiece.
n. In organ-building, a powerful reed stop with a trumpet-like tone.
Word Usage
"The wooden serpent has gone out of use in military bands within recollection, the ophicleide from orchestras only recently."