The Collaborative International Dictionary
Cornopean
Cornopean \Cor*no"pe*an\ (k?r-n?"p?-an), n. (Mus.) An obsolete name for the cornet-[`a]-piston.
Wiktionary
cornopean
n. (context music obsolete English) A large valved horn or trumpet, similar to the orchestral cornet (cornet-à-piston).