zillion vs million

zillion and million both are nouns.

Word	Noun	Adjective	Verb	Adverb
zillion	Yes	Yes	No	No
million	Yes	Yes	No	No

As nouns, zillion and million are synonyms defined as:

Other synonyms of zillion include bazillion, billion, gazillion, jillion, trillion.

zillion (noun)	million (noun)
a very large indefinite number (usually hyperbole)	the number that is represented as a one followed by 6 zeros
	a very large indefinite number (usually hyperbole)

zillion (adjective)	million (adjective)
very large indeterminate number	(in Roman numerals, M written with a macron over it) denoting a quantity consisting of 1,000,000 items or units