What does "damper" mean?

Damper: That which damps or checks; as: (a) A valve or movable plate in the flue or other part of a stove, furnace, etc., used to check or regulate the draught of air. (b) A contrivance, as in a pianoforte, to deaden vibrations; or, as in other pieces of mechanism, to check some action at a particular time. Nor did Sabrina's presence seem to act as any damper at the modest little festivities. W. Black.