From Longman Dictionary of Contemporary Englishsure thingsure thingspoken informalYES used to agree to something ‘Can you pick me up later?’ ‘Sure thing.’ → sure
Examples from the Corpus
sure thing• Elbert cautioned, however, that funding is far from a sure thing.• In either case, the outcome is pretty much a sure thing.• The only sure thing in Iowa is that nothing is sure.• That gives you an idea of how much of a sure thing Lyubov Klochko turned out to be on Sunday.• Helen has no inhibitions about mixing woods, or making sure things match in style or period.• Kip was sure things were going to turn out great.• They wanted instant access, just to make sure things were in place.• Our idea was that at last we could have a real go at it, make sure things worked out. 