As a native English speaker I have to look up words all the time. One of the best and worst things about English as a language is that it’s actually constantly evolving. It also takes words from other languages and authors have a penchant from just making up words depending on what type of literature you read. I wouldn’t worry so much about reading fast. I understand it can be frustrating. But sometimes words being a mystery is part of the experience. I read a lot of sci-fi and there’s a lot of times that authors will just simply make up a word or concept. There can be an etymology for it based on some sort of like Sumerian text or random stuff like that. So don’t stress it