fourth (adj., n.)

"next in order after the third; an ordinal numeral; being one of four equal parts into which a whole is regarded as divided;" mid-15c., alteration (by influence of four), of ferthe, from Old English feorða "fourth," from Proto-Germanic *feurthan (source also of Old Saxon fiortho, Old Norse fiorðe, Dutch vierde, Old High German fiordo, German vierte); see four + -th (1). As a noun from 1590s, both of fractions and in music.

Among the old Quakers, who rejected the pagan weekday names, fourth day was Wednesday, often a secondary day of meeting for worship. Fourth-dimension attested from 1844. The theatrical fourth wall is from 1807. The celebration of the Fourth of July as the epoch of American independence is attested from 1777.

That there is due to Daniel Smith, of the city tavern, for his bill of expences of Congress, on the 4 of July last, including a balance of an old account, the sum of 729 68/90 dollars; also a bill for materials, workmanship, &c furnished for the fire works on the 4 July, the sum of 102 69/90 dollars .... [Auditor General's report, Aug. 8, 1777, Journals of Congress, vol. VII]

updated on August 18, 2020

Definitions of fourth from WordNet
fourth (n.)
following the third position; number four in a countable series;
fourth (n.)
one of four equal parts;
Synonyms: one-fourth / one-quarter / quarter / fourth part / twenty-five percent / quartern
fourth (n.)
the musical interval between one note and another four notes away from it;
fourth (adv.)
in the fourth place;
Synonyms: fourthly
fourth (adj.)
coming next after the third and just before the fifth in position or time or degree or magnitude;
Synonyms: th / quaternary
Etymologies are not definitions. From, not affiliated with etymonline.