a.  1.  Next in order after the fourth;  the ordinal of five.  
2.  Consisting of one of five equal divisions of a thing.
 
n.  1.  The quotient of a unit divided by five; one of five equal parts; a fifth part.  
2.  (Mus.) The interval of three tones and a semitone, embracing five diatonic degrees of the scale; the dominant of any key. 
Noun  1.  fifth  a quantity of liquor equal to one fifth of a United States gallon 
2.  fifth  position five in a countable series of things; "he was fifth out of several hundred runners"  
3.  fifth  a fifth part  
4.  fifth  the musical interval between one note and another five notes away from it  
Adj.  1.  fifth  coming next after the fourth and just before the sixth in position Synonyms: 5th 
Fifth  An enhanced version of FORTH. M.S. Dissertation, Cliff Click
