The Collaborative International Dictionary of English v.0.48:

Fifth \Fifth\, a. [OE. fifte, fifthe, AS. f[imac]fta. See
   Five.]
   1. Next in order after the fourth; -- the ordinal of five.
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   2. Consisting of one of five equal divisions of a thing.
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   Fifth monarchy men (Hist.), a fanatical sect in England, of
      the time of the commonwealth, who maintained that there
      would be a fifth universal monarchy, during which Christ
      would reign on earth a thousand years.

   Fifth wheel, a horizontal wheel or segment above the fore
      axle of a carriage and beneath the body, forming an
      extended support to prevent careening.
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