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Meaning of retarder

re•tard•er

Pronunciation: (ri-tär'dur), [key]
— n.
  1. a person or thing that retards.
    1. any substance added to rubber to delay or prevent vulcanization.
    2. any substance added to delay a process.
  2. an admixture of concrete or plaster that retards its set.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.