[1] : The Collaborative International Dictionary of English v.0.48

fourth \fourth\, n.
   1. one of four equal parts into which one whole may be
      divided; the quotient of a unit divided by four.
      1913 webster

   2. mus. the interval of two tones and a semitone, embracing
      four diatonic degrees of the scale; the subdominant of any
      key.
      1913 webster

   3. one coming next in order after the third.
      1913 webster

   the fourth, specifically, in the united states, the fourth
      day of july, the anniversary of the declaration of
      american independence; as, to celebrate the fourth.
      1913 webster
see also:
the fourth 

[2] : The Collaborative International Dictionary of English v.0.48

fourth \fourth\, a. oe. fourthe, ferthe, feorthe, as.
   fe'oretha, fr. fe'ower four.
   1. next in order after the third; the ordinal of four.
      1913 webster

   2. forming one of four equal parts into which anything may be
      divided.
      1913 webster

[3] : WordNet (r) 2.0

fourth
     adj : coming next after the third and just before the fifth in
           position or time or degree or magnitude; "the
           quaternary period of geologic time extends from the end
           of the tertiary period to the present" syn: 4th, quaternary
     n 1: following the third position; number four in a countable
          series
     2: one of four equal parts; "a quarter of a pound" syn: one-fourth,
         quarter, fourth part, twenty-five percent, quartern
     3: the musical interval between one note and another four notes
        away from it
     adv : in the fourth place; "fourthly, you must pay the rent on the
           first of the month" syn: fourthly
see also:
4th quaternary one-fourth quarter fourth part twenty-five percent 
quartern fourthly 

[4] : Moby Thesaurus II by Grady Ward, 1.0

36 moby thesaurus words for "fourth":
   consecutive intervals, degree, diapason, diatessaron,
   diatonic interval, diatonic semitone, enharmonic diesis,
   enharmonic interval, farthing, fifth, fourth part, half step,
   halftone, interval, less semitone, melodic interval, note, octave,
   one-fourth, parallel octaves, quart, quarter, quartern, quarto,
   second, semitone, seventh, sixth, step, third, tone,
   twenty-five cents, twenty-five percent, two bits, unison interval,
   whole step

Fourth >> F Words
Fourth, definition of term: Fourth
fourth_pag1.html

Fourth Power >> F Words
Fourth Power, definition of term: Fourth Power
fourth+power_pag1.html

Fourth Generati >> F Words
Fourth Generati, definition of term: Fourth Generati
fourth+generati_pag1.html

Fourth Estate >> F Words
Fourth Estate, definition of term: Fourth Estate
fourth+estate_pag1.html

The Fourth Esta >> T Words
The Fourth Esta, definition of term: The Fourth Esta
the+fourth+esta_pag1.html