fourth adj : coming next after the third and just before the fifth in position or time or degree or magnitude; "the quaternary period of geologic time extends from the end of the tertiary period to the present" [syn: 4th, quaternary] (noun)
1: following the third position; number four in a countable series
2: one of four equal parts; "a quarter of a pound" [syn: one-fourth, quarter, fourth part, twenty-five percent, quartern]
3: the musical interval between one note and another four notes away from it adv : in the fourth place; "fourthly, you must pay the rent on the first of the month" [syn: fourthly]