fourth vs quartern

fourth and quartern both are nouns.

Word	Noun	Adjective	Verb	Adverb
fourth	Yes	Yes	No	Yes
quartern	Yes	No	No	No

As nouns, fourth and quartern are synonyms defined as:

Other synonyms of fourth include fourth part, one-fourth, one-quarter, quarter, twenty-five percent.

fourth (noun)	quartern (noun)
the musical interval between one note and another four notes away from it	one of four equal parts
one of four equal parts
following the third position; number four in a countable series

fourth (adjective)	quartern (adjective)
coming next after the third and just before the fifth in position or time or degree or magnitude

fourth (adverb)	quartern (adverb)
in the fourth place