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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).