na-adjective
Expresses subjective certainty or conviction about a fact or situation. Often used in the form 確かな + noun or 確かに + verb.
彼が来るかどうかは確かではない。
It's not certain whether he will come.
確かな証
We need definite proof.
na-adjective
reliable; trustworthy; accurate
Describes a person, information, or method that can be trusted or relied upon. Often used with nouns like 情報, 筋, 方法.
確かな筋からの情報です。
This is information from a reliable source.
彼は確かな技術を持っている。
He has reliable skills.
adverb
if I remember correctly; if I'm not mistaken
Adverbial use, often at the beginning of a sentence, to express a recollection that the speaker is not 100% sure about. Commonly used as 確か〜.
確か、彼は去年引っ越したはずだ。
If I remember correctly, he moved last year.
確か、会議は3時からだったと思う。
If I'm not mistaken, the meeting was from 3 o'clock.