It depends on the context, but the common words are 확실하다(a), 확실하게/확실히(adv), and 정확하다. - 확실하게 말해 줘 - Tell me specifically / Tell me for sure. - 걔가 뭐라 했는지 정확히 말해 봐 - Tell me what that boy said exactly. - 확실히/정확히 말하면, 저는 반대입니다 - To be specific, I am against it.