twenty percent vs fifth part

twenty percent and fifth part both are nouns.

Word	Noun	Adjective	Verb	Adverb
twenty percent	Yes	No	No	No
fifth part	Yes	No	No	No

As nouns, twenty percent and fifth part are synonyms defined as:

Other synonyms of twenty percent include fifth, one-fifth.

twenty percent (noun)	fifth part (noun)
one part in five equal parts	one part in five equal parts