a movable iron plate that regulates the draft in a stove or chimney or furnace
Something that damps or checks:
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.
comparative form of damp: more damp
The word damper comes from the verb damp plus the suffix -er. First recorded in 1825, it originally referred to something that damps the appetite.