There are very few words in the KJV that an average person won't know the meaning of and most of those meanings can be figured out by the context of the sentences.
Peradventure a person can't understand using that method, they can always look up the word in an English dictionary.
Interesting that you use "peradventure" (correctly, I would add)... another of the KJVo's thought it was a verb. Context alone wasn't enough to teach him.