Hi. Opaque doesn’t really mean ambiguous or arcane to me. Without looking in a dictionary it means the opposite of transparent. Transparent = something you can see through or into Opaque = something you cannot see through or into. In the physical world the glass of a typical window is transparent. But if you can’t see through a window because it’s made of a different material we might call it opaque. We then take that term out of the physical world into other areas. For instance if we speak of a person, maybe there’s a person who never lets others know what they’re really thinking. We may say that person is opaque. I can see how an arcane text might be thought of as opaque. But not something that is ambiguous. As for how to remember it. When a word is difficult to remember I try to think of a silly way to remember it. For example I might say the rhyme “my cake is opaque” (cake rhymes with opaque). And cake is indeed opaque. This little silly rhyme may help you remember it. Or you can think of your own silly way to remember it. Good luck!