それ以外、つまり冒険者の半数以上は未だLV1のもとで燃え燻っている。
I am having trouble understanding the last part of this sentence. What does のもとで do here?
Also, how do you figure out the exact meaning of compound words? I tried looking up 燃え燻る but I can't find it in a dictionary. The story I'm reading has a lot of these words that I can't find in a dictionary.
Thanks!