damp·er 
/ˈdæmpɚ/ noun
plural damp·ers /ˈdæmpɚ/ noun [count] 1 : a flat piece of metal in a fireplace, furnace, etc., that controls the amount of air that can enter
▪ Close the damper. 2 : a small piece of wood inside a piano that is covered with cloth and that stops the movement of a piano string
▪ Close the damper.
put a damper on
: to make (something) less strong, active, or exciting
▪ His bad mood put a damper on the celebration. ▪ The rain put a damper on our plans for a picnic. ▪ He was putting a bit of a damper on her spirits.
▪ His bad mood put a damper on the celebration. ▪ The rain put a damper on our plans for a picnic. ▪ He was putting a bit of a damper on her spirits.
