Source : Webster's Revised Unabridged Dictionary (1913)

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.