The Collaborative International Dictionary of English v.0.48:

Retardation \Re`tar*da"tion\, n. [L. retardatio: cf. F.
   retardation.]
   1. The act of retarding; hindrance; the act of delaying; as,
      the retardation of the motion of a ship; -- opposed to
      acceleration.
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            The retardations of our fluent motion. --De Quinsey.
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   2. That which retards; an obstacle; an obstruction.
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            Hills, sloughs, and other terrestrial retardations.
                                                  --Sir W.
                                                  Scott.
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   3. (Mus.) The keeping back of an approaching consonant chord
      by prolonging one or more tones of a previous chord into
      the intermediate chord which follows; -- differing from
      suspension by resolving upwards instead of downwards.
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   4. The extent to which anything is retarded; the amount of
      retarding or delay.
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   Retardation of the tide.
      (a) The lunitidal interval, or the hour angle of the moon
          at the time of high tide any port; the interval
          between the transit of the moon and the time of high
          tide next following.
      (b) The age of the tide; the retard of the tide. See under
          Retard, n.
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