half-dozen vs vi

half-dozen and vi both are adjectives.

Word	Noun	Adjective	Verb	Adverb
half-dozen	No	Yes	No	No
vi	No	Yes	No	No

As adjectives, half-dozen and vi are synonyms defined as:

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

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