retarder
  遲縮劑
  Re·tard·er n.
  1. One who, or that which, retards.
  2. Steam Boiler Any of various devices, as a helix of flat metal strip, introduced into a boiler tube to increase the heating effect of the fire.
  3.  Photog. A substance, as potassium bromide, added to a developer to retard its action.
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