What is the meaning of fourth?

noun

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

adjective

• Coming next after the third and just before the fifth in position or time or degree or magnitude.
  • usage: "the quaternary period of geologic time extends from the end of the tertiary period to the present"
  • synonyms: 4th, quaternary

adverb

• In the fourth place.
  • usage: "fourthly, you must pay the rent on the first of the month"
  • synonyms: fourthly