for sure

Từ điển Oxford Advanced Learner 8th

for ˈsure idiom
(informal)without doubt
• No one knows for sure what happened.
• I think he'll be back on Monday, but I can't say for sure.
•One thing is for sure — it's not going to be easy.
• (NAmE)‘Will you be there?’ ‘For sure.’
Main entry: ↑sure_idiom