vi vs six

vi is not a noun while six is a noun.

Word	Noun	Adjective	Verb	Adverb
vi	No	Yes	No	No
six	Yes	Yes	No	No

As adjectives, vi and six are synonyms defined as:

Other synonyms of vi include 6, half-dozen, half dozen.

vi (noun)	six (noun)
	a playing card or domino or die whose upward face shows six pips
	the cardinal number that is the sum of five and one

vi (adjective)	six (adjective)
denoting a quantity consisting of six items or units	denoting a quantity consisting of six items or units