damper
/ˈdæmpə(r); `dæmpɚ/ n
1 movable metal plate that controls the flow of air into a fire in a stove, furnace, etc 气门; 气闸.
2 small pad that is pressed against a piano-string to stop it vibrating 制音器（终止钢琴弦震动的小毡块）.
3 (idm 习语) put a damper on sth (infml 口) cause (an event, atmosphere, etc) to be less cheerful, excited, etc 使（事情、 气氛等）受到抑制, 减弱
Their argument put a bit of a damper on the party. 他们的争论使聚会颇为扫兴.