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sure; certain; positive; definite
reliable; trustworthy; safe; sound; firm; accurate; correct; exact
If I'm not mistaken; If I remember correctly; If I remember rightly
確かにその通りだけど、もう少し考えたい。
That's certainly true, but I'd like to think about it more.
彼は確かな腕を持つ職人だ。
He's a craftsman with reliable skills.
確か彼は来ると言っていた。
I'm pretty sure he said he'd come.