surely vs for sure

surely is not an adjective while for sure is an adjective.

Word	Noun	Adjective	Verb	Adverb
surely	No	No	No	Yes
for sure	No	Yes	No	Yes

As adverbs, surely and for sure are synonyms defined as:

surely and for sure: definitely or positively (`sure' is sometimes used informally for `surely')

Other synonyms of surely include certainly, for certain, sure, sure as shooting, sure enough.

surely (adjective)	for sure (adjective)
	not open to doubt

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