the.com/damper

means A damper is anything that reduces or stops a vibration, oscillation, or enthusiasm — whether a mechanical device absorbing motion, a flap controlling airflow in a chimney or duct, or a felt pad that silences a piano string.

from From the verb 'damp,' which long before it meant 'moist' meant something closer to 'to choke or stifle' — its older sense links to a Middle Dutch and Middle Low German word 'damp,' meaning vapor, steam, or noxious fume (think of the 'firedamp' that suffocated miners). To 'damp' something was to smother it like a fire choked by gas, and a 'damper' became the thing that does the smothering — first literally over flames and chimney drafts, then figuratively over moods and spirits, and finally over the vibrations of strings and springs.