say-so vs authorisation

say-so and authorisation both are nouns.

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

As nouns, say-so and authorisation are synonyms defined as:

say-so and authorisation: the power or right to give orders or make decisions

Other synonyms of say-so include authority, authorization, dominance, potency.

say-so (noun)	authorisation (noun)
the power or right to give orders or make decisions	the act of conferring legality or sanction or formal warrant
an authoritative declaration	the power or right to give orders or make decisions
one chap's arbitrary assertion	official permission or approval
	a document giving an official instruction or command