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1. Coming next after the third and just before the fifth in position, time, degree or magnitude
   "the fourth period of geologic time extends from the end of the tertiary period to the present";
   - 4th, quaternary

1. In the fourth place
   - fourthly

1. Following the third position; number four in a countable series
    
2. One of four equal parts
   "a fourth of a pound";
   - one-fourth, one-quarter, quarter, fourth part, twenty-five percent, quartern
    
3. The musical interval between one note and another four notes away from it

Sounds like: fouls, fourth, forth, F

Derived forms: fourths

See also: ordinal

Type of: common fraction, interval, musical interval, rank, simple fraction, vulgar fraction [Brit]

Encyclopedia: Fourth, fifth, and sixth derivatives of position