certain vs assurance

certain is not a noun while assurance is a noun.

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

certain (noun)	assurance (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

certain (adjective)	assurance (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