The Collaborative International Dictionary
Melopiano
Melopiano \Mel`o*pi*a"no\, n. [Gr. me`los song + E. piano.] A piano having a mechanical attachment which enables the player to prolong the notes at will.
Wiktionary
melopiano
n. (context musici English) A type of piano in which a system of hammers allows a note to be prolonged indefintely