for sure
For sure (adverb) means Without any doubt; certainly. Example: “I can't say for sure whether the shop is open on Sundays.”
How to use for sure
Learner’s notesIn plain EnglishSomething you say when you are certain, or to say yes.
Conversational. As an interjection it is especially common in North American and Australian speech; formal writing uses certainly or with certainty instead.
"That's for sure" at the end of a sentence adds emphatic agreement with what has just been said.
Fill the gap
Can you complete this real example?
I can't say _____ whether the shop is open on Sundays.