authority vs certain

authority is a noun but certain is not a noun.

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

authority (noun)	certain (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

authority (adjective)	certain (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