hexad vs half a dozen

hexad and half a dozen both are nouns.

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

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

hexad and half a dozen: the cardinal number that is the sum of five and one

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

hexad (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