Interesting concept, but 100 words is really quite a lot to get through... It's tiresome trudging through the easy words at the start, and I never got to see the interesting words before getting bored.

I've seen other systems like this calibrate far more quickly by assigning a sort of score and confidence behind the scenes. Confidence starts out low and increases over time - correct/incorrect answers rapidly adjust score at the beginning, then things settle down.

In practice this means you get a sequence of increasingly uncommon words initially, until you get one wrong, then you drop back to something easier until you start getting things right again, and eventually circle around words at your level.

Also - too many clicks per word. It's low stakes, just let me click the definition once and I'll live if I misclick (or add an undo button).