damper (n.)

"one who or that which dampens," 1748, in the figurative sense, in reference to spirits, enthusiasm, etc., agent noun from damp (v.). In mechanical senses, "device for checking action:" 1783 in reference to a felt-covered piece of wood, etc., which deadens the string after the note is played; 1788 of a chimney, stove, etc., "metal plate in the flue used to control combustion by regulating the draft." Either or both reinforced the figurative senses. The piano damper-pedal (1848) raises the dampers of all the strings so the notes are prolonged and sympathetic vibrations produced.