6 vs half a dozen

6 and half a dozen both are nouns.

Word	Noun	Adjective	Verb	Adverb
6	Yes	Yes	No	No
half a dozen	Yes	No	No	No

As nouns, 6 and half a dozen are synonyms defined as:

Other synonyms of 6 include Captain Hicks, hexad, sestet, sextet, sextuplet, sise, six, sixer, VI.

6 (noun)	half a dozen (noun)
the cardinal number that is the sum of five and one	the cardinal number that is the sum of five and one

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