fifth part vs fifth

fifth part and fifth both are nouns.

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

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

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

fifth part (noun)	fifth (noun)
one part in five equal parts	the musical interval between one note and another five notes away from it
	one part in five equal parts
	a quantity of liquor equal to one fifth of a United States gallon
	position five in a countable series of things

fifth part (adjective)	fifth (adjective)
	coming next after the fourth and just before the sixth in position