surety vs sure thing

surety and sure thing both are nouns.

Word	Noun	Adjective	Verb	Adverb
surety	Yes	No	No	No
sure thing	Yes	No	No	No

As nouns, sure thing is a hypernym of surety; that is, sure thing is a word with a broader meaning than surety:

Other hypernyms of surety include certainty, foregone conclusion.

surety (noun)	sure thing (noun)
something clearly established	something that is certain
a guarantee that an obligation will be met
one who provides a warrant or guarantee to another
a prisoner who is held by one party to insure that another party will meet specified terms
property that your creditor can claim in case you default on your obligation