for certain (=for sure)
用作副词的意思:确实,肯定,当然,无疑地
用法及例句:He is for certain a nerd.他着实叫人讨厌。
When he asked if I'd do it,I said for sure I would.他问我干不干,我说我当然愿意干。
英汉词典参考:
for
certain
sure