fourth: the ordinal number, the one that comes after the third; also a fourth part, one quarter.
This is the plain counting word for "fourth." It orders things in a sequence: the fourth day of creation, the fourth year of a king, the fourth river, the fourth chariot, the fourth generation. Wherever a list or a stretch of time is being numbered, this is the word that marks position number four.
The same word also names a fraction. Used as a noun, it means "a fourth part," that is, one quarter of something. The Bible uses it this way most often in the rules for offerings, where a drink offering calls for a quarter of a measuring jar of wine or oil, and once for splitting a day into quarters. The two uses are really one idea seen from two sides: counting up to the fourth item, or cutting a whole into four parts and taking one of them.
Nothing about the word is unusual or contested. It behaves like an ordinary number, and English carries it over without loss.