ipse dixit vs averment

ipse dixit and averment both are nouns.

Word	Noun	Adjective	Verb	Adverb
ipse dixit	Yes	No	No	No
averment	Yes	No	No	No

As nouns, averment is a hypernym of ipse dixit; that is, averment is a word with a broader meaning than ipse dixit:

ipse dixit: an unsupported dogmatic assertion
averment: a declaration that is made emphatically (as if no supporting evidence were necessary)

Other hypernyms of ipse dixit include assertion, asseveration.

ipse dixit (noun)	averment (noun)
an unsupported dogmatic assertion	a declaration that is made emphatically (as if no supporting evidence were necessary)