affirmation vs say-so

affirmation and say-so both are nouns.

Word	Noun	Adjective	Verb	Adverb
affirmation	Yes	No	No	No
say-so	Yes	No	No	No

As nouns, say-so is a hyponym of affirmation; that is, say-so is a word with a more specific, narrower meaning than affirmation:

affirmation (noun)	say-so (noun)
a judgment by a higher court that the judgment of a lower court was correct and should stand	the power or right to give orders or make decisions
a statement asserting the existence or the truth of something	an authoritative declaration
(religion) a solemn declaration that serves the same purpose as an oath (if an oath is objectionable to the person on religious or ethical grounds)	one chap's arbitrary assertion
the act of affirming or asserting or stating something