fourth fourth /ˈfɔrθ/

adjective

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

adverb

1. () In the fourth place  ( fourthly , fourth )
   in the fourth place
    Fourthly, you must pay the rent on the first of the month
   fourthly, you must pay the rent on the first of the month
   

noun

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