avowal vs asseveration

avowal and asseveration both are nouns.

Word	Noun	Adjective	Verb	Adverb
avowal	Yes	No	No	No
asseveration	Yes	No	No	No

As nouns, asseveration is a hypernym of avowal; that is, asseveration is a word with a broader meaning than avowal:

avowal: a statement asserting the existence or the truth of something
asseveration: a declaration that is made emphatically (as if no supporting evidence were necessary)

Other hypernyms of avowal include assertion, averment.

avowal (noun)	asseveration (noun)
a statement asserting the existence or the truth of something	a declaration that is made emphatically (as if no supporting evidence were necessary)