retarder

One who retards; that which serves as a hindrance, impediment, or cause of retardation.

An obstruction, usually in the form of a twisted piece of sheet-metal, placed in a boiler-flue to retard the hot gases and make them give up their heat to the water in the boiler.

A device, such as a dash-pot, for checking the too rapid motion of any mechanism.

One who, or that which, retards.

Any of various devices, as a helix of flat metal strip, introduced into a boiler tube to increase the heating effect of the fire.