Suppose I was born and use AAA as a native language, then later I want to learn BBB language. It is pretty straightforward that when I encounter an unknown word in BBB, I can look up the word using BBB->AAA dictionary. But then I realized that when I don't know a word in AAA, I can just use AAA->AAA dictionary just fine. Why not I try to use BBB->BBB dictionary too...
So, how many "basic" words in BBB language should I acquired in order to look up the dictionary in that language, the BBB->BBB dictionary? Are there a comprehensive list of those "basic" words?
For example, if I don't know the meaning of "heart", and the dictionary said it is "an organ to pump blood". But now I don't know the word "blood" too, so I look it up and see its definition as "liquid pumped by heart". That would be a mutual definition, which don't help me in actually understand the word "heart" and "blood" at all. So either "heart" or "blood" is a basic word which I must known before using this dictionary. (I guess the real dictionary would avoid this as much as possible???)