The Collaborative International Dictionary of English v.0.48:

dashpot \dash"pot`\, dash-pot \dash-pot\(d[a^]sh"p[o^]t`), n.
   (Mach.)
   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.
   [1913 Webster + WordNet 1.5]

   Note: 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.
         [1913 Webster]

   Note: A cataract of an engine is sometimes called a dashpot.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cataract \Cat"a*ract\, n. [L. cataracta, catarracles, a
   waterfall, Gr. ?, ?, fr. ? to break down; in the passive, to
   fall or rush down (of tumors) to burst; kata` down + ? to
   break.]
   1. A great fall of water over a precipice; a large waterfall.
      [1913 Webster]

   2. (Surg.) An opacity of the crystalline lens, or of its
      capsule, which prevents the passage of the rays of light
      and impairs or destroys the sight.
      [1913 Webster]

   3. (Mach.) A kind of hydraulic brake for regulating the
      action of pumping engines and other machines; -- sometimes
      called dashpot.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dash-pot
    n 1: a mechanical damper; the vibrating part is attached to a
         piston that moves in a chamber filled with liquid