dashpot
dashpot (dash"pot`) , noun
(Machinery) a mechanical damping device containing a piston that moves in a fluid-filled chamber to serve as a pneumatic or hydraulic cushion for a falling weight, as in the valve gear of a steam engine, to prevent shock.
It consists of a chamber, containing air or a liquid, in which a piston (a), attached to the weight, falls freely until it enters a space (as below the openings, b) from which the air or liquid can escape but slowly (as through cock c), when its fall is gradually checked.
A cataract of an engine is sometimes called a dashpot.
Also: dash-pot