assurance vs certain

assurance is a noun but certain is not a noun.

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

assurance (noun)	certain (noun)
freedom from doubt; belief in yourself and your abilities
a statement intended to inspire confidence
a binding commitment to do or give or refrain from something
a British term for some kinds of insurance

assurance (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