certainly vs certain

certainly is not an adjective while certain is an adjective.

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

certainly (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

certainly (adverb)	certain (adverb)
definitely or positively (`sure' is sometimes used informally for `surely')