damper
n//ˈdæmpɚ//dämpare, spjäll
A contrivance (sordine), as in a pianoforte, to deaden vibrations; or, as in other pieces of mechanism, to check some action at a particular time.
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.