Cornet-a-piston \Cor"net-[`a]-pis`ton\ (k?r"n?t-?-p?s"t?n; F. k?r`n?`?p?s`{t?n}"), n.; pl. {Cornets-[`a]-piston}. [F.] (Mus.) A brass wind instrument, like the trumpet, furnished with valves moved by small pistons or sliding rods; a cornopean; a cornet.