I'm attempting to learn some basic Japanese vocabulary through a set of Anki flash cards, but one of the cards has the word かなり on it. The definition provided says "fairly, rather." This implies to me that it shows something to be of a lesser degree. For example, if I am fairly certain of something, I am not certain of it, but believe myself to be correct. On the other hand, Wiktionary define かなり as "quite." This seems much stronger than "fairly" or "rather." At least as I use it, "quite" implies a very high degree. If I am quite certain of something, there is little to no doubt in my mind. If someone asks me if I am certain of something, I would not hesitate to confirm by saying "Yes, I am quite certain." Tagaini Jisho suggests a definition of "Considerably, fairly, quite." Sadly, I find each of these words to be different. "Quite" seems stronger than "considerably," which seems much stronger than fairly.
Given all of this, I am left confused as to what かなり actually means. Can someone explain it to me?