E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Damper (A).
A snap before dinner, which damps or takes off the edge of appetite. Thats a damper also means a wet-blanket influence, a rebuff which damps or cools ones courage.
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Also a large thin cake of flour and water baked in hot ashes. The mute of a stringed instrument to deaden the sound is also called a damper.