certain vs authority

certain is not a noun while authority is a noun.

Word	Noun	Adjective	Verb	Adverb
certain	No	Yes	No	No
authority	Yes	No	No	No

certain (noun)	authority (noun)
	the power or right to give orders or make decisions
	official permission or approval
	freedom from doubt; belief in yourself and your abilities
	an authoritative written work
	an administrative unit of government
	an expert whose views are taken as definitive
	(usually plural) persons who exercise (administrative) control over others

certain (adjective)	authority (adjective)
established beyond doubt or question; definitely known
having or feeling no doubt or uncertainty; confident and assured
certain to occur; destined or inevitable
established irrevocably
exercising or taking care great enough to bring assurance
definite but not specified or identified
reliable in operation or effect