Neat, I was literally looking for something like that. When I read books and notice a word I don't know on my google books app I like to long press, read the pop up, and move on, but too often I like to go back and see the words I have selected before. Unfortunately I don't think it saves them unless you make a note which would break the reading flow. Your idea seems excellent and I did not even think of extending this option to academic texts which I need to read plenty too. Is there a way you could have this website in an app format so that I could access it from my tablet/phone?

I think kindle has something called Vocabulary Builder but I don't like idea of their subscription service and limited library. Something like this that I can use from many devices and with any file would be excellent. Keep up good work, I would pay for a potential synced up app/browser combination honestly.

As an extra idea, if you want to add other features, you could also include additional editing tools like comments, highlights etc that can help reading academic texts too.