Na-adjective (keiyodoshi)
sure; certain; positive; definite
彼が間違っているのは確かです。It is certain that he is wrong. reliable; trustworthy; safe; sound; firm; accurate; correct; exact
Adverb (fukushi)
If I'm not mistaken; If I remember correctly; If I remember rightly
Also written 確【たしか】、慥か【たしか】