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

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "fifth":
   consecutive intervals, decimalization, decimation, degree,
   diapason, diatessaron, diatonic interval, diatonic semitone,
   enharmonic diesis, enharmonic interval, fivefold, fourth,
   half step, halftone, interval, less semitone, melodic interval,
   note, octave, parallel octaves, pentad, pentadic, pentastyle,
   pentavalent, quinary, quincuncial, quinquefid, quinquennial,
   quinquepartite, quinquepartition, quinquesection, quintuple,
   quintuplicate, second, semitone, seventh, sextipartition, sixth,
   step, tenth, third, tithe, tone, unison interval, whole step



The Free On-line Dictionary of Computing (30 December 2018):

Fifth

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