attest vs avow

attest and avow both are verbs.

Word	Noun	Adjective	Verb	Adverb
attest	No	No	Yes	No
avow	No	No	Yes	No

As verbs, avow is a hypernym of attest; that is, avow is a word with a broader meaning than attest:

attest: authenticate, affirm to be true, genuine, or correct, as in an official capacity
avow: to declare or affirm solemnly and formally as true

Other hypernyms of attest include affirm, assert, aver, swan, swear, verify.

attest (verb)	avow (verb)
authenticate, affirm to be true, genuine, or correct, as in an official capacity	to declare or affirm solemnly and formally as true
provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes	admit openly and bluntly; make no bones about
give testimony in a court of law
establish or verify the usage of