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.
      [1913 Webster]

   2. Consisting of one of five equal divisions of a thing.
      [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fifth \Fifth\, n.
   1. The quotient of a unit divided by five; one of five equal
      parts; a fifth part.
      [1913 Webster]

   2. (Mus.) The interval of three tones and a semitone,
      embracing five diatonic degrees of the scale; the dominant
      of any key.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fifth
    adj 1: coming next after the fourth and just before the sixth in
           position [syn: fifth, 5th]
    n 1: a quantity of liquor equal to one fifth of a United States
         gallon
    2: position five in a countable series of things; "he was fifth
       out of several hundred runners"
    3: one part in five equal parts [syn: one-fifth, fifth,
       fifth part, twenty percent]
    4: the musical interval between one note and another five notes
       away from it

The Free On-line Dictionary of Computing (19 January 2023):

Fifth

   An enhanced version of FORTH.  M.S. Dissertation, Cliff Click
   , Texas A&M, 1985.  Available from the
   Software Construction Co, (409)696-5432.