{adv. phr.} 1. Without doubt; certainly; surely. * /He couldn't tell for sure from a distance whether it was George or Tom./ * /He didn't know for certain which bus to take./ * /I know for certain that he has a car./ 2. {slang} Certain. * /"That car is smashed so badly it's no good any more." "That's for sure!"/ Compare: SURE THING.
See: FOR SURE.