Retarder may refer to: Retarder (album), an album by The Unband Retarder (chemistry), a chemical agent that slows down a chemical reaction Retarder (mechanical engineering), a device for slowing down large trucks, lorries, buses, coaches and other vehicles Retarder (railroad), a device to slow railroad freight cars as they are sorted into trains Acrylic retarder, a chemical agent added to fine art acrylic paint to slow its short drying time Dough retarder, a refrigerator used to slow down proofing of yeast when making dough Retardation plate, an optical device that alters the polarization state of a light wave traveling through it See also Retardation (disambiguation)