ETYM Old Eng. fifte, fifthe, AS. fîfta. Related to Five.
Coming next after the fourth and just before the sixth in position; SYN. 5th.

1. A quantity of liquor equal to one fifth of a United States gallon.
2. Position five in a countable series of things.

In music, an interval of five diatonic notes, consisting of three whole tones and a semitone, for example C–G. A fifth is an example of a ��perfect interval” because it remains the same in both major and minor keys. A fifth may be augmented (by one semitone), for example C–G sharp, or diminished (by one semitone), for example C–G flat.
The musical interval between one note and another five notes away from it.